missing_syscall: drop raw_getpid()

This used to be relevant since in old versions of glibc an internal
cache is maintained, while we might sidestep their invalidation
with raw_clone(). After glibc 2.25 getpid() is a trivial wrapper
for the syscall, and hence there's no need to have a separate
raw_getpid().

src/basic/missing_syscall.h

@@ -63,16 +63,6 @@ static inline int missing_ioprio_set(int which, int who, int ioprio) {
 
 /* ======================================================================= */
 
-static inline pid_t raw_getpid(void) {
-#if defined(__alpha__)
-        return (pid_t) syscall(__NR_getxpid);
-#else
-        return (pid_t) syscall(__NR_getpid);
-#endif
-}
-
-/* ======================================================================= */
-
 #if !HAVE_KCMP
 static inline int missing_kcmp(pid_t pid1, pid_t pid2, int type, unsigned long idx1, unsigned long idx2) {
         return syscall(__NR_kcmp, pid1, pid2, type, idx1, idx2);