regex: fix a SIZE_MAX macro redefinition warning

regex: fix a SIZE_MAX macro redefinition warning

Since commit 56a1a3ab ("Silence GCC's \"cast of pointer to integer of a
different size\" warning", 26-10-2015), sparse has been issuing a macro
redefinition warning for the SIZE_MAX macro. However, gcc did not issue
any such warning.

After commit 56a1a3ab, in terms of the order of #includes and #defines,
the code looked something like:

  $ cat -n junk.c
       1	#include <stddef.h>
       2
       3	#define SIZE_MAX ((size_t) -1)
       4
       5	#include <stdint.h>
       6
       7	int main(int argc, char *argv[])
       8	{
       9		return 0;
      10	}
  $
  $ gcc junk.c
  $

However, if you compile that file with -Wsystem-headers, then it will
also issue a warning. Having set -Wsystem-headers in CFLAGS, using the
config.mak file, then (on cygwin):

  $ make compat/regex/regex.o
      CC compat/regex/regex.o
  In file included from /usr/lib/gcc/x86_64-pc-cygwin/4.9.3/include/stdint.h:9:0,
                   from compat/regex/regcomp.c:21,
                   from compat/regex/regex.c:77:
  /usr/include/stdint.h:362:0: warning: "SIZE_MAX" redefined
   #define SIZE_MAX (__SIZE_MAX__)
   ^
  In file included from compat/regex/regex.c:69:0:
  compat/regex/regex_internal.h:108:0: note: this is the location of the previous definition
   # define SIZE_MAX ((size_t) -1)
   ^
  $

The compilation of the compat/regex code is somewhat unusual in that the
regex.c file directly #includes the other c files (regcomp.c, regexec.c
and regex_internal.c). Commit 56a1a3ab added an #include of <stdint.h>
to the regcomp.c file, which results in the redefinition, since this is
included after the regex_internal.h header. This header file contains a
'fallback' definition for SIZE_MAX, in order to support systems which do
not have the <stdint.h> header (the HAVE_STDINT_H macro is not defined).

In order to suppress the warning, we move the #include of <stdint.h>
from regcomp.c to the start of the compilation unit, close to the top
of regex.c, prior to the #include of the regex_internal.h header.

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>