cmake: Test gcc toolchain is support armv7-a or not

Signed-off-by: sndnvaps <sndnvaps@gmail.com>

CMakeLists.txt

@@ -1,6 +1,10 @@
 cmake_minimum_required(VERSION 2.8)
 project(WiringPi_lib)
 
+include(CheckCCompilerFlag)
+CHECK_C_COMPILER_FLAG("-march=armv7-a" COMPILER_SUPPORT_ARMV7_A)
+if (COMPILER_SUPPORT_ARMV7_A)
+	MESSAGE("GCC Support armv7-a")
 add_subdirectory(devLib)
 add_subdirectory(gpio)
 #add_subdirectory(pins)
@@ -20,3 +24,7 @@ SET(CPACK_PACKAGE_DESCRIPTION "WiringPi Library for RaspberryPi")
 SET(CPACK_PACKAGE_CONTACT "sndnvaps@gmail.com")
 INCLUDE(CPack)
 
+else( not COMPILER_SUPPORT_ARMV7_A)
+	MESSAGE("GCC Not support armv7-a")
+	MESSAGE("You need to use Cross-Compiler to build it")
+endif()