build: set language to C++

Set the language in the build to C++.

Change-Id: I997d6a697bc6c98ab208518a81e66ac2aa7945c1
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index 58df3e0..2c88b97 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6,6 +6,7 @@
 AC_CONFIG_AUX_DIR([build-aux])
 AM_INIT_AUTOMAKE([subdir-objects -Wall -Werror foreign dist-xz])
 AM_SILENT_RULES([yes])
+AC_LANG([C++])
 
 # Make sure the default CFLAGS of `-O2 -g` don't override CODE_COVERAGE_CFLAGS
 # It is important that this comes before AC_PROG_C{C,XX}, as we are attempting
@@ -89,7 +90,6 @@
 
     AX_SAVE_FLAGS_WITH_PREFIX(OLD, [CPPFLAGS])
     AX_APPEND_COMPILE_FLAGS([$GTEST_CFLAGS], [CPPFLAGS])
-    AC_LANG_PUSH([C++])
     AC_CHECK_HEADERS([gtest/gtest.h], [
         AS_IF([test "x$GTEST_CFLAGS" = "x"], [
             AS_IF([test "x$PTHREAD_CFLAGS" = "x"], [
@@ -104,18 +104,15 @@
             AC_MSG_ERROR([Testing enabled but could not find gtest/gtest.h])
         ])
     ])
-    AC_LANG_POP([C++])
     AX_RESTORE_FLAGS_WITH_PREFIX(OLD, [CPPFLAGS])
 
     AX_SAVE_FLAGS_WITH_PREFIX(OLD, [CPPFLAGS])
     AX_APPEND_COMPILE_FLAGS([$GMOCK_CFLAGS], [CPPFLAGS])
-    AC_LANG_PUSH([C++])
     AC_CHECK_HEADERS([gmock/gmock.h], [], [
         AS_IF([test "x$enable_tests" = "xyes"], [
             AC_MSG_ERROR([Testing enabled but could not find gmock/gmock.h])
         ])
     ])
-    AC_LANG_POP([C++])
     AX_RESTORE_FLAGS_WITH_PREFIX(OLD, [CPPFLAGS])
 
     AX_SAVE_FLAGS_WITH_PREFIX(OLD, [LDFLAGS])