Prevent arm-runtime CMake arguments persisting over loops (#587)

The additional_cmake_args variable is used to override the defaults and
disable testing so that it can be controlled by the higher-level CMake
project. But the variable is currently set only when the tests should be
disabled. If the tests do not need to be disabled, the value is not
updated and the version from the previous iteration of the loop will be
used, potentially incorrectly disabling the tests.

To fix this, clear the value on every loop if not needed.

Author: dcandler

arm-multilib/CMakeLists.txt

@@ -136,6 +136,7 @@ math(EXPR lib_count_dec "${lib_count} - 1")
 foreach(lib_idx RANGE ${lib_count_dec})
     string(JSON lib_def GET ${multilib_defs} ${lib_idx})
     string(JSON variant GET ${lib_def} "variant")
+    set(additional_cmake_args "")
 
     if(variant IN_LIST ENABLE_VARIANTS OR ENABLE_VARIANTS STREQUAL "all")
         string(JSON variant_multilib_flags GET ${lib_def} "flags")
@@ -164,7 +165,7 @@ foreach(lib_idx RANGE ${lib_count_dec})
             # FVP testing should default to off, so override any 
             # settings from the JSON.
             if(test_executor STREQUAL "fvp" AND NOT ${ENABLE_FVP_TESTING})
-                set(additional_cmake_args "-DENABLE_LIBC_TESTS=OFF" "-DENABLE_COMPILER_RT_TESTS=OFF" "-DENABLE_LIBCXX_TESTS=OFF")
+                list(APPEND additional_cmake_args "-DENABLE_LIBC_TESTS=OFF" "-DENABLE_COMPILER_RT_TESTS=OFF" "-DENABLE_LIBCXX_TESTS=OFF")
                 set(read_ENABLE_LIBC_TESTS "OFF")
                 set(read_ENABLE_COMPILER_RT_TESTS "OFF")
                 set(read_ENABLE_LIBCXX_TESTS "OFF")