Merge pull request #466 from apple/kwt-ubuntu1804-clang-workaround

Workaround for Ubuntu 18.04 clang crashes in swift-corelibs-libdispath

Signed-off-by: Kim Topley <ktopley@apple.com>

Author: shahmishal

PATCHES

@@ -484,3 +484,4 @@ github commits starting with 29bdc2f from
 [6e1825a] APPLIED rdar://54572081
 [319bd33] APPLIED rdar://54572081
 [6c5b3ba] APPLIED rdar://54572081
+[7e7677b] APPLIED rdar://54572081