builtin: fix GetFinalPathNameByHandleW declaration for TCC on Windows

TCC''s bundled windows.h does not chain-include fileapi.h, so
GetFinalPathNameByHandleW had no C declaration in scope when TCC
compiled any program that pulled in builtin. TCC (in C99 mode)
treats implicit function declarations as hard errors.

Add an explicit #include <fileapi.h> inside a $if windows {} block
alongside the function declaration. V already passes
thirdparty/tcc/include/winapi to TCC''s include search path, so TCC
resolves the declaration from its own bundled header (which carries
the correct DWORD WINAPI signature). GCC and MSVC receive a harmless
redundant include since fileapi.h has include guards.

Keeping the declaration in $if windows {} also stops it from being
compiled into Linux/macOS builds, where the symbol does not exist.

Co-Authored-By: WOZCODE <contact@withwoz.com>

Author: PythonWillRule

vlib/builtin/cfns.c.v

@@ -295,7 +295,11 @@ fn C.CreateFile(lpFilename &u16, dwDesiredAccess u32, dwShareMode u32, lpSecurit
 fn C.CreateFileW(lpFilename &u16, dwDesiredAccess u32, dwShareMode u32, lpSecurityAttributes &u16, dwCreationDisposition u32,
 	dwFlagsAndAttributes u32, hTemplateFile voidptr) voidptr
 
-fn C.GetFinalPathNameByHandleW(hFile voidptr, lpFilePath &u16, nSize u32, dwFlags u32) u32
+$if windows {
+	#include <fileapi.h>
+
+	fn C.GetFinalPathNameByHandleW(hFile voidptr, lpFilePath &u16, nSize u32, dwFlags u32) u32
+}
 
 fn C.CreatePipe(hReadPipe &voidptr, hWritePipe &voidptr, lpPipeAttributes voidptr, nSize u32) bool