Allow disabling "inline"

Compiler support for inline is sometimes buggy, and occasionally
missing entirely.  This patch adds a test for inline support, and
redefines the keyword with the preprocessor if necessary at compile
time.

Signed-off-by: Gary V. Vaughan <gary@thewrittenword.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

configure.ac

@@ -327,6 +327,12 @@ GIT_PARSE_WITH(tcltk))
 AC_MSG_NOTICE([CHECKS for programs])
 #
 AC_PROG_CC([cc gcc])
+AC_C_INLINE
+case $ac_cv_c_inline in
+  inline | yes | no)	;;
+  *)			AC_SUBST([INLINE], [$ac_cv_c_inline]) ;;
+esac
+
 # which switch to pass runtime path to dynamic libraries to the linker
 AC_CACHE_CHECK([if linker supports -R], git_cv_ld_dashr, [
    SAVE_LDFLAGS="${LDFLAGS}"