[Bug #20494] Search non-default directories for GMP

Co-Authored-by: lish82 (Hiroki Katagiri)

configure.ac

@@ -16,6 +16,7 @@ m4_include([tool/m4/ruby_append_option.m4])dnl
 m4_include([tool/m4/ruby_append_options.m4])dnl
 m4_include([tool/m4/ruby_check_builtin_func.m4])dnl
 m4_include([tool/m4/ruby_check_builtin_setjmp.m4])dnl
+m4_include([tool/m4/ruby_check_header.m4])dnl
 m4_include([tool/m4/ruby_check_printf_prefix.m4])dnl
 m4_include([tool/m4/ruby_check_setjmp.m4])dnl
 m4_include([tool/m4/ruby_check_signedness.m4])dnl
@@ -1375,7 +1376,7 @@ AS_CASE("$target_cpu", [x64|x86_64|i[3-6]86*], [
 RUBY_UNIVERSAL_CHECK_HEADER([x86_64, i386], x86intrin.h)
 
 AS_IF([test "x$with_gmp" != xno],
-  [AC_CHECK_HEADERS(gmp.h)
+  [RUBY_CHECK_HEADER(gmp.h)
    AS_IF([test "x$ac_cv_header_gmp_h" != xno],
      AC_SEARCH_LIBS([__gmpz_init], [gmp],
        [AC_DEFINE(HAVE_LIBGMP, 1)]))])

tool/m4/ruby_check_header.m4

@@ -0,0 +1,8 @@
+dnl -*- Autoconf -*-
+AC_DEFUN([RUBY_CHECK_HEADER],
+    [# RUBY_CHECK_HEADER($@)
+    save_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS m4_if([$5], [], [$INCFLAGS], [$5])"
+    AC_CHECK_HEADER([$1], [$2], [$3], [$4])
+    CPPFLAGS="$save_CPPFLAGS"
+    unset save_CPPFLAGS])