[PATCH] Compile out all pretty stack trace support when LLVM is built without support for backtraces.

[Chandler Carruth]

This patch seems fine, feel free to submit. Some nits below on the code.

For future reference to anyone who looks up the code review down the road though, I'm not really endorsing us restricting raw TLS to optional components. But there is no reason to force sorting that out in the general case today.


================
Comment at: lib/Support/PrettyStackTrace.cpp:35
@@ -34,2 +34,3 @@
 // FIXME: This should be moved to a Compiler.h abstraction.
+#if ENABLE_BACKTRACE
 #ifdef _MSC_VER // MSVC supports this with a __declspec.
----------------
Start this before the big comment block and give it its own comment indicating that this is used to avoid using thread locals where possible?

================
Comment at: lib/Support/PrettyStackTrace.cpp:159-161
@@ -146,3 +158,5 @@
 void LLVMEnablePrettyStackTrace() {
+#if ENABLE_BACKTRACE
   EnablePrettyStackTrace();
+#endif
 }
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No real need for these, although no harm.

http://reviews.llvm.org/D7242

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