Update GCC except.S to support ARMC6

ARM Compiler 6 supports GNU-style assembly with armclang. Instead of
relying on armasm with the legacy syntax, GCC except.S is updated so
that it can be used with ARM as well as GCC_ARM toolchains. CMake is
updated to use this version.

Author: wernerlewis

platform/source/TARGET_CORTEX_M/CMakeLists.txt

@@ -1,11 +1,7 @@
 # Copyright (c) 2020-2021 ARM Limited. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-if(${MBED_TOOLCHAIN} STREQUAL "GCC_ARM")
-    target_sources(mbed-core INTERFACE TOOLCHAIN_GCC/except.S)
-elseif(${MBED_TOOLCHAIN} STREQUAL "ARM")
-    target_sources(mbed-core INTERFACE TOOLCHAIN_ARM/except.S)
-endif()
+target_sources(mbed-core INTERFACE TOOLCHAIN_GCC/except.S)
 
 target_sources(mbed-core
     INTERFACE

platform/source/TARGET_CORTEX_M/TOOLCHAIN_GCC/except.S

@@ -105,7 +105,11 @@ UsageFault_Handler:
 Fault_Handler:
 #if (DOMAIN_NS == 1)
 #if MBED_CONF_PLATFORM_CRASH_CAPTURE_ENABLED
+#if defined(__ARMCC_VERSION)
+#define mbed_fault_context Image$$RW_m_crash_data$$ZI$$Base
+#else
 #define mbed_fault_context __CRASH_DATA_RAM_START__
+#endif
 #endif
 
         MOV     R12,R3