Disable annoying Clang warnings

* configure.ac (CHECK_LISP_OBJECT_TYPE): Disable
-Wimplicit-const-int-float-conversion and -Wint-in-bool-context, which
currently only have false positives.

configure.ac

@@ -1105,6 +1105,8 @@ AS_IF([test $gl_gcc_warnings = no],
   if test "$emacs_cv_clang" = yes; then
     gl_WARN_ADD([-Wno-missing-braces])
     gl_WARN_ADD([-Wno-null-pointer-arithmetic])
+    gl_WARN_ADD([-Wno-implicit-const-int-float-conversion])
+    gl_WARN_ADD([-Wno-int-in-bool-context])
   fi
 
   # This causes too much noise in the MinGW build