bfd: Define ___lc_codepage_func prototype for older MinGW-w64

In commit 68e80d96a8, the usage of
___lc_codepage_func was introduced to determine the current encoding.

Prior to version 9.0 of MinGW-w64, the function prototype for
___lc_codepage_func was missing and trying to build BFD caused the
following error:

error: implicit declaration of function ‘___lc_codepage_func’

This changeset adds a conditonal definition of
___lc_codepage_func to allow a sucessful build with MinGW-w64.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>

bfd/bfdio.c

@@ -31,6 +31,11 @@
 #include <locale.h>
 #endif
 
+#if defined(__MINGW64_VERSION_MAJOR) && __MINGW64_VERSION_MAJOR < 9
+/* This prototype was added to locale.h in version 9.0 of MinGW-w64.  */
+_CRTIMP unsigned int __cdecl ___lc_codepage_func(void);
+#endif
+
 #ifndef S_IXUSR
 #define S_IXUSR 0100    /* Execute by owner.  */
 #endif