[PATCH] Remove support for runtime multithreading

[Ed Maste]

================
Comment at: lib/Support/ErrorHandling.cpp:74
@@ +73,3 @@
+    // The LLVM error handler is likely to call exit(), which should not be done
+    // under a mutex (some mutex implementations exhibit undefined behavior if
+    // destroyed while acquired).  So the mutex is acquired only while reading
----------------
To be pedantic, all implementations exhibit undefined behaviour if a mutex destroyed while owned, although the nature of that behavior may be different.

http://reviews.llvm.org/D4139