crt: Add double underscore prefix to internal symbols

Signed-off-by: Martin Storsjö <martin@martin.st>

mingw-w64-crt/crt/crtexe.c

diff --git a/mingw-w64-crt/crt/crtexe.c b/mingw-w64-crt/crt/crtexe.c
index a7af136..8b1c863 100644
--- a/mingw-w64-crt/crt/crtexe.c
+++ b/mingw-w64-crt/crt/crtexe.c
@@ -99,8 +99,8 @@
 
 static int __cdecl pre_c_init (void);
 static void __cdecl pre_cpp_init (void);
-_CRTALLOC(".CRT$XIAA") _PIFV mingw_pcinit = pre_c_init;
-_CRTALLOC(".CRT$XCAA") _PVFV mingw_pcppinit = pre_cpp_init;
+_CRTALLOC(".CRT$XIAA") _PIFV __mingw_pcinit = pre_c_init;
+_CRTALLOC(".CRT$XCAA") _PVFV __mingw_pcppinit = pre_cpp_init;
 
 extern int _MINGW_INSTALL_DEBUG_MATHERR;