[ATFE] Enable COMPILER_RT_EXCLUDE_LIBC_PROVIDED_ARM_AEABI_BUILTINS in the ATFE to exclude libc-provided AEABI builtins.

We don't want two implementations of the __aeabi runtime
in two different libraries. We could suppress the compiler-rt
implementation at build time so there's only the picolibc definition.
This patch llvm/llvm-project#137952
introduced a new cmake flag called
COMPILER_RT_EXCLUDE_LIBC_PROVIDED_ARM_AEABI_BUILTINS to support
this functionality.

When enabled, this flag excludes the following ARM AEABI memory
function implementations from the compiler-rt build:
__aeabi_memcmp
__aeabi_memset
__aeabi_memcpy
__aeabi_memmove

These functions are already provided by standard C libraries like
newlib, and picolibc, so excluding them avoids duplicate symbol
definitions and reduces unnecessary code duplication.

Also we can now remove the downstream patch that changed the
library order to put -lc before compiler-rt builtins as there is
now this recent upstream addition of the
COMPILER_RT_EXCLUDE_LIBC_PROVIDED_ARM_AEABI_BUILTINS flag.

Author: simpal01

arm-software/embedded/arm-runtimes/CMakeLists.txt

@@ -296,6 +296,7 @@ ExternalProject_Add(
     -DCOMPILER_RT_BUILD_SANITIZERS=OFF
     -DCOMPILER_RT_BUILD_XRAY=OFF
     -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON
+    -DCOMPILER_RT_EXCLUDE_LIBC_PROVIDED_ARM_AEABI_BUILTINS=ON
     -DLLVM_CMAKE_DIR=${LLVM_BINARY_DIR}
     -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
     ${compiler_rt_test_cmake_args}