[AIX] Add -pthread to build on AIX (#129108)
When building in tree clang without having `-pthread` we get a bunch of
`Assertion failed: FD != kInvalidFile && "Invalid or inactive file
descriptor"` when testing check-clang.
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index 9a5cd1d..c5d3e23 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -1189,6 +1189,7 @@
if (UNIX AND ${CMAKE_SYSTEM_NAME} MATCHES "AIX")
add_compile_definitions(_XOPEN_SOURCE=700)
add_compile_definitions(_LARGE_FILE_API)
+ add_compile_options(-pthread)
# Modules should be built with -shared -Wl,-G, so we can use runtime linking
# with plugins.
