configure: refuse to build with jemalloc when header is missing

[ruby-core:90964] [Bug #15520]

Freom: Misty De Meo <mistydemeo@github.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66779 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.ac

@@ -1095,7 +1095,8 @@ AS_IF([test "x$with_jemalloc" != xno],[
     [test x$with_jemalloc = xyes && with_jemalloc=no])
   AC_CHECK_HEADER(jemalloc/jemalloc.h, [
     AC_DEFINE(RUBY_ALTERNATIVE_MALLOC_HEADER, [<jemalloc/jemalloc.h>])
-  ])
+  ],
+  [test x$with_jemalloc = xyes && with_jemalloc=no])
   AS_IF([test "x$with_jemalloc" != xyes], [
     AC_CACHE_CHECK([for jemalloc with JEMALLOC_MANGLE], rb_cv_jemalloc_demangle,
       [AC_LINK_IFELSE([AC_LANG_PROGRAM([@%:@define JEMALLOC_MANGLE 1