[libcxxabi] Allow explicit pthread opt-in

[bcraig]

Summary

Companion to http://reviews.llvm.org/D20573

When building libcxxabi in tree (i.e. in llvm/projects/libcxxabi, along with llvm/projects/libcxx), libcxx's config_site.in doesn't get created in a timely manner. This means that any configuration that is normally set in libcxx's config_site.in needs to be duplicated in libcxxabi to successfully build libcxxabi. This patch does exactly that for the _LIBCPP_HAS_THREAD_API_PTHREAD preprocessor define.

[rmaprath]

CMakeLists.txt

278

Shouldn't there be an option() line for this new build option? Also a check for compatibility with the LIBCXXABI_ENABLE_THREADS option?

[rmaprath]

LGTM.

(I don't have powers to accept libcxx patches in general, but this patch is quite small and related to something I plugged in, so, I think it's OK in this instance)

[bcraig]

r270732

CMakeLists.txt

 option(LIBCXXABI_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
 option(LIBCXXABI_ENABLE_THREADS "Build with threads enabled" ON)
+option(LIBCXXABI_HAS_PTHREAD_API "Ignore auto-detection and force use of pthread API" OFF)
 set(LIBCXXABI_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
 set(LIBCXXABI_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
 

 endif()
 
 if (NOT LIBCXXABI_ENABLE_THREADS)
+  if (LIBCXXABI_HAS_PTHREAD_API)
+    message(FATAL_ERROR "LIBCXXABI_HAS_PTHREAD_API can only"
+                        " be set to ON when LIBCXXABI_ENABLE_THREADS"
+                        " is also set to ON.")
+  endif()
   add_definitions(-DLIBCXXABI_HAS_NO_THREADS=1)
 endif()
 
+if (LIBCXXABI_HAS_PTHREAD_API)
+  add_definitions(-D_LIBCPP_HAS_THREAD_API_PTHREAD)
+endif()
+
 # This is the _ONLY_ place where add_definitions is called.
 if (MSVC)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)