Fix macro-redefinition warning on MSVC.

In commit 9d6b160, I tweaked pg_config.h.win32 to use
"#define HAVE_LONG_LONG_INT_64 1" rather than defining it as empty,
for consistency with what happens in an autoconf'd build.
But Solution.pm injects another definition of that macro into
ecpg_config.h, leading to justifiable (though harmless) compiler whining.
Make that one consistent too.  Back-patch, like the previous patch.

Discussion: https://postgr.es/m/CAEepm=1dWsXROuSbRg8PbKLh0S=8Ou-V8sr05DxmJOF5chBxqQ@mail.gmail.com

Author: tglsfdc

src/tools/msvc/Solution.pm

@@ -419,7 +419,7 @@ s{PG_VERSION_STR "[^"]+"}{__STRINGIFY(x) #x\n#define __STRINGIFY2(z) __STRINGIFY
 		  || confess "Could not open ecpg_config.h";
 		print O <<EOF;
 #if (_MSC_VER > 1200)
-#define HAVE_LONG_LONG_INT_64
+#define HAVE_LONG_LONG_INT_64 1
 #define ENABLE_THREAD_SAFETY 1
 EOF
 		print O "#define USE_INTEGER_DATETIMES 1\n"