build: allow compilation on cygwin

Gnulib is incompatible with -Wunused-macros.  Addtionally,
cygwin 1.7.1 coupled with --enable-gcc-warnings tripped on:

grep.c: In function 'print_line_middle':
grep.c:805: error: array subscript has type 'char' [-Wchar-subscripts]
grep.c: In function 'main':
grep.c:1833: error: 'optarg' redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
grep.c:1834: error: 'optind' redeclared without dllimport attribute after being referenced with dll linkage

* configure.ac (GNULIB_WARN_FLAGS): Disable -Wunused-macros.
* src/grep.c (print_line_middle): Use correct type to tolower.
(main): Drop useless redeclarations.
* .gitignore: Ignore more built files.

Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/src/grep.c b/src/grep.c
index 8193bc55..f4cd8757 100644
--- a/src/grep.c
+++ b/src/grep.c
@@ -802,7 +802,7 @@ print_line_middle (const char *beg, const char *lim,
       /* This can't possibly be correct with UTF-8,
 	 but it's equivalent to what was there so far.  */
       while (--i >= 0)
-	buf[i] = tolower(beg[i]);
+	buf[i] = tolower((unsigned char) beg[i]);
     }
   else
     {
@@ -1830,8 +1830,6 @@ main (int argc, char **argv)
   int opt, cc, status;
   int default_context;
   FILE *fp;
-  extern char *optarg;
-  extern int optind;
 
   initialize_main (&argc, &argv);
   set_program_name (argv[0]);