Add shim for fork() on PS4

[dyung]

Summary

Add a shim for fork() since it is not supported on the PS4 platform.

[probinson]

LGTM

compiler-rt/lib/profile/InstrProfilingUtil.h

 int lprofUnlockFd(int fd);
 int lprofLockFileHandle(FILE *F);
 int lprofUnlockFileHandle(FILE *F);
 
 /*! Open file \c Filename for read+write with write
  * lock for exclusive access. The caller will block
  * if the lock is already held by another process. */
 FILE *lprofOpenFileEx(const char *Filename);
-/* PS4 doesn't have setenv/getenv. Define a shim. */
+/* PS4 doesn't have setenv/getenv/fork. Define a shim. */
 #if __ORBIS__
 static inline char *getenv(const char *name) { return NULL; }
 static inline int setenv(const char *name, const char *value, int overwrite)
 { return 0; }
+static pid_t fork() { return -1; }
 #endif /* #if __ORBIS__ */
 
 /* GCOV_PREFIX and GCOV_PREFIX_STRIP support */
 /* Return the path prefix specified by GCOV_PREFIX environment variable.
  * If GCOV_PREFIX_STRIP is also specified, the strip level (integer value)
  * is returned via \c *PrefixStrip. The prefix length is stored in *PrefixLen.
  */
 const char *lprofGetPathPrefix(int *PrefixStrip, size_t *PrefixLen);