compiler-rt: re-exec with ASLR disabled when necessary

Some sanitizers (at least msan) currently require ASLR to be disabled.
When we detect that ASLR is enabled, re-exec with it disabled rather
than exiting with an error.  See LLVM GitHub issue 53256 for more
detail: llvm/llvm-project#53256

No objection:	dim
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D33934

(cherry picked from commit 930a7c2)

contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

@@ -2197,8 +2197,11 @@ void CheckASLR() {
   }
   if ((aslr_status & PROC_ASLR_ACTIVE) != 0) {
     Printf("This sanitizer is not compatible with enabled ASLR "
-           "and binaries compiled with PIE\n");
-    Die();
+           "and binaries compiled with PIE\n"
+           "ASLR will be disabled and the program re-executed.\n");
+    int aslr_ctl = PROC_ASLR_FORCE_DISABLE;
+    CHECK_NE(procctl(P_PID, 0, PROC_ASLR_CTL, &aslr_ctl), -1);
+    ReExec();
   }
 #else
   // Do nothing