[docs] Add some architectures into the list of supported ThreadSanitizer platforms

Some platforms for which TSAN has build rules are omitted for the lack of
known build bots.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@355445 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ThreadSanitizer.rst

@@ -19,10 +19,10 @@ Supported Platforms
 
 ThreadSanitizer is supported on the following OS:
 
-* Android
-* Darwin
+* Android aarch64, x86_64
+* Darwin arm64, x86_64
 * FreeBSD
-* Linux
+* Linux aarch64, x86_64, powerpc64, powerpc64le
 * NetBSD
 
 Support for other 64-bit architectures is possible, contributions are welcome.