fix --with-gmp (broken by r57490)

Looking at the generated shell script (also the autoconf manual), it
seems AC_SEARCH_LIBS() m4 macro does not define HAVE_LIBsomething C
preprocessor macros, unlike AC_CHECK_LIB() which does define them.
This previous change effectively killed building with GMP because
building that mode depends on existence of HAVE_LIBGMP. [Bug #13402]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58254 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.in

@@ -1386,13 +1386,15 @@ AC_ARG_WITH([gmp],
 AS_IF([test "x$with_gmp" != xno],
   [AC_CHECK_HEADERS(gmp.h)
    AS_IF([test "x$ac_cv_header_gmp_h" != xno],
-     AC_SEARCH_LIBS([__gmpz_init], [gmp]))])
+     AC_SEARCH_LIBS([__gmpz_init], [gmp],
+       [AC_DEFINE(HAVE_LIBGMP, 1)]))])
 
 AC_ARG_WITH([jemalloc],
   [AS_HELP_STRING([--with-jemalloc],[use jemalloc allocator])],
   [with_jemalloc=$withval], [with_jemalloc=no])
 AS_IF([test "x$with_jemalloc" = xyes],[
-  AC_SEARCH_LIBS([malloc_conf], [jemalloc], [], [with_jemalloc=no])
+  AC_SEARCH_LIBS([malloc_conf], [jemalloc],
+    [AC_DEFINE(HAVE_LIBJEMALLOC, 1)], [with_jemalloc=no])
   AC_CHECK_HEADER(jemalloc/jemalloc.h, [
     AC_DEFINE(RUBY_ALTERNATIVE_MALLOC_HEADER, [<jemalloc/jemalloc.h>])
   ])