Fix minor build problems related to MinGW64.

 configure.ac: Read $srcdir/nt/mingw-cfg.site when $MSYSTEM is
 "MINGW64" as well.

 nt/inc/ms-w32.h (pthread_sigmask): Undefine if defined, for MinGW64.

 src/unexw32.c (_start) [__MINGW64__]: Define to __start.

2 files changed, 11 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 556fcce5fa5..637164281d4 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2014-01-11  Fabrice Popineau  <fabrice.popineau@gmail.com>
+
+        * unexw32.c (_start) [__MINGW64__]: Define to __start.
+
 2014-01-11  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (try_window_id): Don't use this function's optimizations
diff --git a/src/unexw32.c b/src/unexw32.c
index 5411cd2a95c..f70cdd79478 100644
--- a/src/unexw32.c
+++ b/src/unexw32.c
@@ -85,6 +85,13 @@ DWORD_PTR  extra_bss_size_static = 0;
 
 PIMAGE_SECTION_HEADER heap_section;
 
+/* MinGW64 doesn't add a leading underscore to external symbols,
+   whereas configure.ac sets up LD_SWITCH_SYSTEM_TEMACS to force the
+   entry point at __start, with two underscores.  */
+#ifdef __MINGW64__
+#define _start __start
+#endif
+
 /* Startup code for running on NT.  When we are running as the dumped
    version, we need to bootstrap our heap and .bss section into our
    address space before we can actually hand off control to the startup