[sanitizers] Fix internal__exit on Solaris

`TestCases/log-path_test.cpp` currently `FAIL`s on Solaris:

  $ env ASAN_OPTIONS=log_path=`for((i=0;i<10000;i++)); do echo -n $i; done`  ./log-path_test.cpp.tmp
  ==5031==ERROR: Path is too long: 01234567...
  Segmentation Fault (core dumped)

The `SEGV` happens here:

  Thread 2 received signal SIGSEGV, Segmentation fault.
  [Switching to Thread 1 (LWP 1)]
  0x00000000 in ?? ()
  (gdb) where
  #0  0x00000000 in ?? ()
  #1  0x080a1e63 in __interceptor__exit (status=1)
      at /vol/gcc/src/llvm/llvm/local/projects/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:3808
  #2  0x08135ea8 in __sanitizer::internal__exit (exitcode=1)
      at /vol/gcc/src/llvm/llvm/local/projects/compiler-rt/lib/sanitizer_common/sanitizer_solaris.cc:139

when `__interceptor__exit` tries to call `__interception::real__exit` which
is `NULL` at this point because the interceptors haven't been initialized yet.

Ultimately, the problem lies elsewhere, however: `internal__exit` in
`sanitizer_solaris.cpp` calls `_exit` itself since there doesn't exit a
non-intercepted version in `libc`.  Using the `syscall` interface instead
isn't usually an option on Solaris because that interface isn't stable.
However, in the case of `SYS_exit` it can be used nonetheless: `SYS_exit`
has remained unchanged since at least Solaris 2.5.1 in 1996, and this is
what this patch does.

Tested on `amd64-pc-solaris2.11`.

Differential Revision: https://reviews.llvm.org/D88404

compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

@@ -426,15 +426,6 @@ uptr internal_sched_yield() {
   return internal_syscall(SYSCALL(sched_yield));
 }
 
-void internal__exit(int exitcode) {
-#if SANITIZER_FREEBSD || SANITIZER_OPENBSD
-  internal_syscall(SYSCALL(exit), exitcode);
-#else
-  internal_syscall(SYSCALL(exit_group), exitcode);
-#endif
-  Die();  // Unreachable.
-}
-
 unsigned int internal_sleep(unsigned int seconds) {
   struct timespec ts;
   ts.tv_sec = seconds;
@@ -451,6 +442,17 @@ uptr internal_execve(const char *filename, char *const argv[],
 }
 #endif  // !SANITIZER_SOLARIS && !SANITIZER_NETBSD
 
+#if !SANITIZER_NETBSD
+void internal__exit(int exitcode) {
+#if SANITIZER_FREEBSD || SANITIZER_OPENBSD || SANITIZER_SOLARIS
+  internal_syscall(SYSCALL(exit), exitcode);
+#else
+  internal_syscall(SYSCALL(exit_group), exitcode);
+#endif
+  Die();  // Unreachable.
+}
+#endif  // !SANITIZER_NETBSD
+
 // ----------------- sanitizer_common.h
 bool FileExists(const char *filename) {
   if (ShouldMockFailureToOpen(filename))

compiler-rt/lib/sanitizer_common/sanitizer_solaris.cpp

@@ -160,10 +160,6 @@ DECLARE__REAL_AND_INTERNAL(uptr, sched_yield, void) {
   return sched_yield();
 }
 
-DECLARE__REAL_AND_INTERNAL(void, _exit, int exitcode) {
-  _exit(exitcode);
-}
-
 DECLARE__REAL_AND_INTERNAL(uptr, execve, const char *filename,
                            char *const argv[], char *const envp[]) {
   return _REAL(execve)(filename, argv, envp);