configure.in: libunwind.h check

* configure.in: check for libunwind.h, which is not available in
  very old OS X SDK.  [ruby-core:71080] [Bug #11591]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52124 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Wed Oct 14 16:56:50 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* configure.in: check for libunwind.h, which is not available in
+	  very old OS X SDK.  [ruby-core:71080] [Bug #11591]
+
 Wed Oct 14 14:11:42 2015  Brian Black  <bblack@veracode.com>
 
 	* iseq.c (rb_insn_operand_intern): change kw in callinfo disasm from the

configure.in

@@ -3210,6 +3210,7 @@ AS_CASE(["$target_cpu-$target_os"],
     AC_CHECK_HEADERS([execinfo.h])
     if test "x$ac_cv_header_execinfo_h" = xyes; then
 	AC_CHECK_LIB([execinfo], [backtrace])
+	AC_CHECK_HEADERS([libunwind.h])
     fi],
 [*-freebsd*|x86_64-netbsd*], [
     AC_CHECK_HEADERS([execinfo.h])

vm_dump.c

@@ -438,7 +438,7 @@ rb_vmdebug_thread_dump_state(VALUE self)
 # ifdef HAVE_LIBUNWIND
 #  undef backtrace
 #  define backtrace unw_backtrace
-# elif defined(__APPLE__) && defined(__x86_64__)
+# elif defined(__APPLE__) && defined(__x86_64__) && defined(HAVE_LIBUNWIND_H)
 #  define UNW_LOCAL_ONLY
 #  include <libunwind.h>
 #  undef backtrace