Makefile & configure: add a NO_FNMATCH_CASEFOLD flag

On some platforms (like Solaris) there is a fnmatch, but it doesn't
support the GNU FNM_CASEFOLD extension that's used by the
jj/icase-directory series' fnmatch_icase wrapper.

Change the Makefile so that it's now possible to set
NO_FNMATCH_CASEFOLD=YesPlease on those systems, and add a configure
probe for it.

Unlike the NO_REGEX check we don't add AC_INCLUDES_DEFAULT to our
headers. This is because on a GNU system the definition of
FNM_CASEFOLD in fnmatch.h is guarded by:

    #if !defined _POSIX_C_SOURCE || _POSIX_C_SOURCE < 2 || defined _GNU_SOURCE

One of the headers AC_INCLUDES_DEFAULT includes ends up defining one
of those, so if we'd use it we'd always get
NO_FNMATCH_CASEFOLD=YesPlease on GNU systems, even though they have
FNM_CASEFOLD.

When checking the flags we use:

    ifdef NO_FNMATCH
    ...
    else
    ifdef NO_FNMATCH_CASEFOLD
    ...
    endif
    endif

The "else" so that we don't link against compat/fnmatch/fnmatch.o
twice if both NO_FNMATCH and NO_FNMATCH_CASEFOLD are defined.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -70,6 +70,9 @@ all::
 #
 # Define NO_FNMATCH if you don't have fnmatch in the C library.
 #
+# Define NO_FNMATCH_CASEFOLD if your fnmatch function doesn't have the
+# FNM_CASEFOLD GNU extension.
+#
 # Define NO_LIBGEN_H if you don't have libgen.h.
 #
 # Define NEEDS_LIBGEN if your libgen needs -lgen when linking
@@ -834,6 +837,7 @@ ifeq ($(uname_S),SunOS)
 	NO_MKDTEMP = YesPlease
 	NO_MKSTEMPS = YesPlease
 	NO_REGEX = YesPlease
+	NO_FNMATCH_CASEFOLD = YesPlease
 	ifeq ($(uname_R),5.6)
 		SOCKLEN_T = int
 		NO_HSTRERROR = YesPlease
@@ -1326,6 +1330,12 @@ ifdef NO_FNMATCH
 	COMPAT_CFLAGS += -Icompat/fnmatch
 	COMPAT_CFLAGS += -DNO_FNMATCH
 	COMPAT_OBJS += compat/fnmatch/fnmatch.o
+else
+ifdef NO_FNMATCH_CASEFOLD
+	COMPAT_CFLAGS += -Icompat/fnmatch
+	COMPAT_CFLAGS += -DNO_FNMATCH_CASEFOLD
+	COMPAT_OBJS += compat/fnmatch/fnmatch.o
+endif
 endif
 ifdef NO_SETENV
 	COMPAT_CFLAGS += -DNO_SETENV

config.mak.in

@@ -47,6 +47,7 @@ NO_C99_FORMAT=@NO_C99_FORMAT@
 NO_HSTRERROR=@NO_HSTRERROR@
 NO_STRCASESTR=@NO_STRCASESTR@
 NO_FNMATCH=@NO_FNMATCH@
+NO_FNMATCH_CASEFOLD=@NO_FNMATCH_CASEFOLD@
 NO_MEMMEM=@NO_MEMMEM@
 NO_STRLCPY=@NO_STRLCPY@
 NO_UINTMAX_T=@NO_UINTMAX_T@

configure.ac

@@ -789,6 +789,28 @@ GIT_CHECK_FUNC(fnmatch,
 [NO_FNMATCH=YesPlease])
 AC_SUBST(NO_FNMATCH)
 #
+# Define NO_FNMATCH_CASEFOLD if your fnmatch function doesn't have the
+# FNM_CASEFOLD GNU extension.
+AC_CACHE_CHECK([whether the fnmatch function supports the FNMATCH_CASEFOLD GNU extension],
+ [ac_cv_c_excellent_fnmatch], [
+AC_EGREP_CPP(yippeeyeswehaveit,
+	AC_LANG_PROGRAM([
+#include <fnmatch.h>
+],
+[#ifdef FNM_CASEFOLD
+yippeeyeswehaveit
+#endif
+]),
+	[ac_cv_c_excellent_fnmatch=yes],
+	[ac_cv_c_excellent_fnmatch=no])
+])
+if test $ac_cv_c_excellent_fnmatch = yes; then
+	NO_FNMATCH_CASEFOLD=
+else
+	NO_FNMATCH_CASEFOLD=YesPlease
+fi
+AC_SUBST(NO_FNMATCH_CASEFOLD)
+#
 # Define NO_MEMMEM if you don't have memmem.
 GIT_CHECK_FUNC(memmem,
 [NO_MEMMEM=],