CMakeLists.txt: Removed force to -march=native

Setting the arch to native for arm.* should not generally be necessary.
If this is absolutely required, it can be passed manually.  Setting
-march=native seems to fail on some versions of gnu gcc for arm.
Removed the force to -march=native in favor of letting cmake set the
arch.

If at some point, this would be required, a better way would be to add
the compile flag after testing if it is supported.

Example:
    upm_add_compile_flags(CXX "-march=native")

Signed-off-by: Noel Eck <noel.eck@intel.com>

CMakeLists.txt

@@ -236,11 +236,6 @@ include (TargetArch)
 target_architecture (DETECTED_ARCH)
 message (STATUS "Target arch is ${DETECTED_ARCH}")
 
-#-march=native for ARM when not defined/forced
-if (DETECTED_ARCH MATCHES "arm.*" AND NOT CMAKE_CXX_FLAGS MATCHES "-march")
-  set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=native")
-endif()
-
 # enable c++11 standards support unconditionally
 include(CheckCXXCompilerFlag)
 if (CMAKE_VERSION VERSION_LESS "3.1")