Improve --enable-gcc-warnings for MinGW64

This partially reverts my 2016-05-30 patch.  Apparently MinGW64
still requires pacifications that GCC 7.1.1 x86-64 (Fedora 26)
does not.  Also, pacify tparam.c, which isn’t used on Fedora.
* lib-src/etags.c (process_file_name, TeX_commands):
* src/buffer.c (fix_overlays_before):
* src/data.c (Fmake_variable_buffer_local, cons_to_unsigned)
(cons_to_signed):
* src/editfns.c (Ftranslate_region_internal):
Prefer UNINIT to some stray value, as this simplifies
code-reading later.
* src/eval.c (CACHEABLE): New macro.
(internal_lisp_condition_case): Use it.
* src/tparam.c (tparam1): Use FALLTHROUGH to pacify GCC.

lib-src/etags.c

@@ -1528,7 +1528,7 @@ process_file_name (char *file, language *lang)
   fdesc *fdp;
   compressor *compr;
   char *compressed_name, *uncompressed_name;
-  char *ext, *real_name = NULL, *tmp_name;
+  char *ext, *real_name UNINIT, *tmp_name;
   int retval;
 
   canonicalize_filename (file);
@@ -5594,7 +5594,7 @@ TeX_commands (FILE *inf)
   linebuffer *key;
 
   char TEX_esc = '\0';
-  char TEX_opgrp = 0, TEX_clgrp = 0;
+  char TEX_opgrp UNINIT, TEX_clgrp UNINIT;
 
   /* Initialize token table once from environment. */
   if (TEX_toktab == NULL)

src/buffer.c

@@ -3764,7 +3764,7 @@ fix_overlays_before (struct buffer *bp, ptrdiff_t prev, ptrdiff_t pos)
   /* If parent is nil, replace overlays_before; otherwise, parent->next.  */
   struct Lisp_Overlay *tail = bp->overlays_before, *parent = NULL, *right_pair;
   Lisp_Object tem;
-  ptrdiff_t end = prev;
+  ptrdiff_t end UNINIT;
 
   /* After the insertion, the several overlays may be in incorrect
      order.  The possibility is that, in the list `overlays_before',

src/data.c

@@ -1823,7 +1823,7 @@ The function `default-value' gets the default value and `set-default' sets it.
   struct Lisp_Symbol *sym;
   struct Lisp_Buffer_Local_Value *blv = NULL;
   union Lisp_Val_Fwd valcontents;
-  bool forwarded = false;
+  bool forwarded UNINIT;
 
   CHECK_SYMBOL (variable);
   sym = XSYMBOL (variable);
@@ -2607,7 +2607,7 @@ uintmax_t
 cons_to_unsigned (Lisp_Object c, uintmax_t max)
 {
   bool valid = false;
-  uintmax_t val = max;
+  uintmax_t val UNINIT;
   if (INTEGERP (c))
     {
       valid = XINT (c) >= 0;
@@ -2661,7 +2661,7 @@ intmax_t
 cons_to_signed (Lisp_Object c, intmax_t min, intmax_t max)
 {
   bool valid = false;
-  intmax_t val = max;
+  intmax_t val UNINIT;
   if (INTEGERP (c))
     {
       val = XINT (c);

src/editfns.c

@@ -3612,8 +3612,9 @@ It returns the number of characters changed.  */)
   cnt = 0;
   for (; pos < end_pos; )
     {
-      register unsigned char *p = BYTE_POS_ADDR (pos_byte);
-      unsigned char *str = tt, buf[MAX_MULTIBYTE_LENGTH];
+      unsigned char *p = BYTE_POS_ADDR (pos_byte);
+      unsigned char *str UNINIT;
+      unsigned char buf[MAX_MULTIBYTE_LENGTH];
       int len, str_len;
       int oc;
       Lisp_Object val;

src/eval.c

@@ -30,6 +30,15 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "dispextern.h"
 #include "buffer.h"
 
+/* CACHEABLE is ordinarily nothing, except it is 'volatile' if
+   necessary to cajole GCC into not warning incorrectly that a
+   variable should be volatile.  */
+#if defined GCC_LINT || defined lint
+# define CACHEABLE volatile
+#else
+# define CACHEABLE /* empty */
+#endif
+
 /* Chain of condition and catch handlers currently in effect.  */
 
 /* struct handler *handlerlist; */
@@ -1226,7 +1235,7 @@ internal_lisp_condition_case (Lisp_Object var, Lisp_Object bodyform,
 			      Lisp_Object handlers)
 {
   struct handler *oldhandlerlist = handlerlist;
-  volatile ptrdiff_t clausenb = 0;
+  ptrdiff_t CACHEABLE clausenb = 0;
 
   CHECK_SYMBOL (var);
 

src/tparam.c

@@ -125,6 +125,7 @@ tparam1 (const char *string, char *outstring, int len,
 		goto onedigit;
 	      if (tem < 100)
 		goto twodigit;
+	      FALLTHROUGH;
 	    case '3':		/* %3 means output in decimal, 3 digits.  */
 	      if (tem > 999)
 		{
@@ -132,6 +133,7 @@ tparam1 (const char *string, char *outstring, int len,
 		  tem %= 1000;
 		}
 	      *op++ = tem / 100 + '0';
+	      FALLTHROUGH;
 	    case '2':		/* %2 means output in decimal, 2 digits.  */
 	    twodigit:
 	      tem %= 100;
@@ -140,10 +142,12 @@ tparam1 (const char *string, char *outstring, int len,
 	      *op++ = tem % 10 + '0';
 	      argp++;
 	      break;
+
             case 'p':           /* %pN means use param N for next subst.  */
 	      tem = fixed_argp[(*p++) - '1'];
 	      explicit_param_p = true;
 	      break;
+
 	    case 'C':
 	      /* For c-100: print quotient of value by 96, if nonzero,
 		 then do like %+.  */
@@ -152,8 +156,10 @@ tparam1 (const char *string, char *outstring, int len,
 		  *op++ = tem / 96;
 		  tem %= 96;
 		}
+	      FALLTHROUGH;
 	    case '+':		/* %+x means add character code of char x.  */
 	      tem += *p++;
+	      FALLTHROUGH;
 	    case '.':		/* %. means output as character.  */
 	      if (left)
 		{
@@ -173,6 +179,7 @@ tparam1 (const char *string, char *outstring, int len,
 		    }
 		}
 	      *op++ = tem ? tem : 0200;
+	      FALLTHROUGH;
 	    case 'f':		/* %f means discard next arg.  */
 	      argp++;
 	      break;