Lib/java/javahead.swg: clean up jlong handling.

As for __int64 definition. __int64 is a non-standard Visual-C-specific
type used in win32/jni_md.h. It is defined by other Win32 compilers in
one way or another, obviously for compatibility. It's more appropriate
to give the compiler a chance to make necessary arrangements instead
of reinventing the wheel. This, giving a chance, can be achieved by
including virtually any standard header. Since jni.h includes stdio.h,
defining __int64 in javahead.swg is redundant. Since doing so actually
triggers compilation errors on MinGW if a system header is included
in the %begin section, it's arguably appropriate to omit it.

As for #undef _LP64 removal. Undefining a pre-defined macro, which
_LP64 is, is bad style, and if followed by inclusion of systems
headers, it's actually error-prone. Log suggests that it was added
to resolve a warning. I'm inclined to believe that it rather was a
misunderstanding of some kind. Or a bug in warning subsystem of
some particular compiler version, in which case it would have been
more appropriate to advise users to ignore the warning.

Lib/java/javahead.swg

@@ -30,18 +30,6 @@
 #endif
 
 %insert(runtime) %{
-/* Fix for jlong on some versions of gcc on Windows */
-#if defined(__GNUC__) && !defined(__INTEL_COMPILER)
-  typedef long long __int64;
-#endif
-
-/* Fix for jlong on 64-bit x86 Solaris */
-#if defined(__x86_64)
-# ifdef _LP64
-#   undef _LP64
-# endif
-#endif
-
 #include <jni.h>
 #include <stdlib.h>
 #include <string.h>