Update the various INSTALL files

* nt/INSTALL.W64:
* nt/INSTALL:
* INSTALL: Update the installation information, in particular the
fact that HarfBuzz is now preferred as the shaping library.

INSTALL

@@ -117,19 +117,25 @@ ADDITIONAL DISTRIBUTION FILES
 
 * Complex Text Layout support libraries
 
-On GNU and Unix systems, Emacs needs the optional libraries "m17n-db",
+On GNU and Unix systems, Emacs needs optional libraries to correctly
-"libm17n-flt", "libotf" to correctly display such complex scripts as
+display such complex scripts as Indic and Khmer, and also for scripts
-Indic and Khmer, and also for scripts that require Arabic shaping
+that require Arabic shaping support (Arabic and Farsi).  If the
-support (Arabic and Farsi).  On some systems, particularly GNU/Linux,
+HarfBuzz library is installed, Emacs will build with it and use it for
-these libraries may be already present or available as additional
+this purpose.  HarfBuzz is the preferred shaping engine, both on Posix
-packages.  Note that if there is a separate 'dev' or 'devel' package,
+hosts and on MS-Windows, so we recommend installing it before building
-for use at compilation time rather than run time, you will need that
+Emacs.  The alternative for GNU/Linux and Posix systems is to use the
-as well as the corresponding run time package; typically the dev
+"m17n-db", "libm17n-flt", and "libotf" libraries.  (On some systems,
-package will contain header files and a library archive.  Otherwise,
+particularly GNU/Linux, these libraries may be already present or
-you can download the libraries from <https://www.nongnu.org/m17n/>.
+available as additional packages.)  Note that if there is a separate
+'dev' or 'devel' package, for use at compilation time rather than run
+time, you will need that as well as the corresponding run time
+package; typically the dev package will contain header files and a
+library archive.  On MS-Windows, if HarfBuzz is not available, Emacs
+will use the Uniscribe shaping engine that is part of the OS.
 
 Note that Emacs cannot support complex scripts on a TTY, unless the
-terminal includes such a support.
+terminal includes such a support.  However, most modern terminal
+emulators, such as xterm, do support such scripts.
 
 * intlfonts-VERSION.tar.gz
 
@@ -234,10 +240,10 @@ directory.  On Red Hat-based systems, the corresponding command is
 config-manager --set-enabled fedora-debuginfo updates-debuginfo').
 
 Once you have installed the source package, for example at
-/path/to/emacs-26.1, add the following line to your startup file:
+/path/to/emacs-27.1, add the following line to your startup file:
 
      (setq find-function-C-source-directory
-           "/path/to/emacs-26.1/src")
+           "/path/to/emacs-27.1/src")
 
 The installation directory of the Emacs source package will contain
 the exact package name and version number Emacs is installed on your
@@ -249,7 +255,7 @@ Emacs debugging symbols are distributed by a debug package.  It does
 not exist for every released Emacs package, this depends on the
 distribution.  On Debian-based systems, you can install a debug
 package of Emacs with a command like 'apt-get install emacs-dbg' (on
-older systems, replace 'emacs' with eg 'emacs25').  On Red Hat-based
+older systems, replace 'emacs' with eg 'emacs27').  On Red Hat-based
 systems, the corresponding command is 'dnf debuginfo-install emacs'.
 
 

nt/INSTALL

@@ -502,11 +502,21 @@ build will run on Windows 9X and newer systems).
        Does Emacs use -lgnutls?                                yes
        Does Emacs use -lxml2?                                  yes
        Does Emacs use -lfreetype?                              no
+       Does Emacs use HarfBuzz?                                yes
        Does Emacs use -lm17n-flt?                              no
        Does Emacs use -lotf?                                   no
        Does Emacs use -lxft?                                   no
+       Does Emacs use -lsystemd?                               no
+       Does Emacs use -ljansson?                               yes
+       Does Emacs use the GMP library?                         yes
        Does Emacs directly use zlib?                           yes
+       Does Emacs have dynamic modules support?                yes
        Does Emacs use toolkit scroll bars?                     yes
+       Does Emacs support Xwidgets?                            no
+       Does Emacs have threading support in lisp?              yes
+       Does Emacs support the portable dumper?                 yes
+       Does Emacs support the legacy unexec dumping?           no
+       Which dumping strategy does Emacs use?                  pdumper
 
   You are almost there, hang on.
 
@@ -815,6 +825,14 @@ build will run on Windows 9X and newer systems).
   the libjansson DLL (for 32-bit builds of Emacs) are available from
   the ezwinports site and from the MSYS2 project.
 
+* Optional support for HarfBuzzz shaping library
+
+  Emacs supports display of complex scripts and Arabic shaping.  The
+  preferred library for that is HarfBuzz; prebuilt binaries are
+  available from the ezwinports site (for 32-bit builds of Emacs) and
+  from the MSYS2 project.  If HarfBuzz is not available, Emacs will
+  use the Uniscribe shaping engine that is part of MS-Windows.
+
 
 This file is part of GNU Emacs.
 

nt/INSTALL.W64

@@ -55,14 +55,16 @@ packages (you can copy and paste it into the shell with Shift + Insert):
   mingw-w64-x86_64-jansson \
   mingw-w64-x86_64-libxml2 \
   mingw-w64-x86_64-gnutls \
-  mingw-w64-x86_64-zlib
+  mingw-w64-x86_64-zlib \
+  mingw-w64-x86_64-harfbuzz
 
 The packages include the base developer tools (autoconf, grep, make, etc.),
 the compiler toolchain (gcc, gdb, etc.), several image libraries, an XML
-library, the GnuTLS (transport layer security) library, and zlib for
+library, the GnuTLS (transport layer security) library, zlib for
-decompressing text.  Only the first three packages are required (base-devel,
+decompressing text, and HarfBuzz for use as the shaping engine.  Only the
-toolchain, xpm-nox); the rest are optional.  You can select only part of the
+first three packages are required (base-devel,  toolchain, xpm-nox); the
-libraries if you don't need them all.
+rest are optional.  You can select only part of the libraries if you don't
+need them all.
 
 You now have a complete build environment for Emacs.