wrappers: Stop specifying -fuse-cxa-atexit

Since clang 9.0.0 (34ec6929a1fb33716d0035dc0f1f164d7568b4dc
in llvm-project), it's no longer necessary to set this to be able
to use __cxa_thread_atexit (for TLS destructors). This brings the
behaviour closer to GCC, and reduces the amount of non-default
options used.

wrappers/clang-target-wrapper.sh

@@ -68,7 +68,6 @@ FLAGS="$FLAGS -target $TARGET"
 FLAGS="$FLAGS -rtlib=compiler-rt"
 FLAGS="$FLAGS -stdlib=libc++"
 FLAGS="$FLAGS -fuse-ld=lld"
-FLAGS="$FLAGS -fuse-cxa-atexit"
 FLAGS="$FLAGS -Qunused-arguments"
 
 $CCACHE "$CLANG" $FLAGS "$@"