Stop passing --disable-threads to LLVM

Author: alexcrichton

configure

@@ -834,9 +834,7 @@ do
         LLVM_TARGET="--target=$t"
 
         # Disable unused LLVM features
-        LLVM_OPTS="$LLVM_DBG_OPTS --disable-docs \
-                   --enable-bindings=none --disable-threads \
-                   --disable-pthreads"
+        LLVM_OPTS="$LLVM_DBG_OPTS --disable-docs --enable-bindings=none"
 
         case "$CFG_C_COMPILER" in
             ("ccache clang")