Merge pull request #14411 from hugueskamba/hk_cmake_fix_cortex_a9_warning

CMake: Fix Cortex-A9 flags for GCC_ARM toolchain

Author: 0xc0170

tools/cmake/cores/Cortex-A9.cmake

@@ -5,9 +5,8 @@ if(${MBED_TOOLCHAIN} STREQUAL "GCC_ARM")
     list(APPEND common_options
         "-mthumb-interwork"
         "-marm"
-        "-march=armv7-a"
         "-mfpu=vfpv3"
-        "-mfloat-abi=hard"
+        "-mfloat-abi=softfp"
         "-mno-unaligned-access"
         "-mcpu=cortex-a9"
     )