Fix clang detection

Port of https://chromium-review.googlesource.com/c/chromiumos/platform2/+/1922532

BUG=chromium:1026028
BUG=chromium:1024392

TEST=clang detection works.

Change-Id: I8ab6fcfc7391b1e3c96d0a30c35f56c44925194c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/webrtc-apm/+/1922908
Reviewed-by: Caroline Tice <cmtice@chromium.org>
Reviewed-by: Hsinyu Chao <hychao@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>

common.mk

diff --git a/common.mk b/common.mk
index 77879d8..3412287 100644
--- a/common.mk
+++ b/common.mk
@@ -266,13 +266,13 @@
 RMDIR ?= rmdir
 ECHO = /bin/echo -e
 
-ifeq ($(lastword $(subst /, ,$(CC))),clang)
+ifeq ($(filter clang,$(subst -, ,$(notdir $(CC)))),clang)
 CDRIVER = clang
 else
 CDRIVER = gcc
 endif
 
-ifeq ($(lastword $(subst /, ,$(CXX))),clang++)
+ifeq ($(filter clang++,$(subst -, ,$(notdir $(CXX)))),clang++)
 CXXDRIVER = clang
 else
 CXXDRIVER = gcc