src/x86/win64.S: Handle name mangling and PIC

Move the macros from unix64.S into a shared header asmnames.h and use
them in win64.S too.

src/x86/asmnames.h

@@ -0,0 +1,30 @@
+#ifndef ASMNAMES_H
+#define ASMNAMES_H
+
+#define C2(X, Y)  X ## Y
+#define C1(X, Y)  C2(X, Y)
+#ifdef __USER_LABEL_PREFIX__
+# define C(X)     C1(__USER_LABEL_PREFIX__, X)
+#else
+# define C(X)     X
+#endif
+
+#ifdef __APPLE__
+# define L(X)     C1(L, X)
+#else
+# define L(X)     C1(.L, X)
+#endif
+
+#if defined(__ELF__) && defined(__PIC__)
+# define PLT(X)	  X@PLT
+#else
+# define PLT(X)	  X
+#endif
+
+#ifdef __ELF__
+# define ENDF(X)  .type	X,@function; .size X, . - X
+#else
+# define ENDF(X)
+#endif
+
+#endif /* ASMNAMES_H */