Clear CXX flags to make test_package work

Conan's adds host side flags to the conan_toolchain.cmake file which
interferes with arm-none-eabi-g++. To fix this, we set CMAKE_CXX_FLAGS
to an empty string, then provide target specific flags to the
executable.

recipes/arm-gnu-toolchain/all/conanfile.py

@@ -92,6 +92,7 @@ def validate(self):
             raise ConanInvalidConfiguration(
                 "The compiler version must be one of the following: "
                 f"{supported_compiler_versions}.")
+
         major_version = str(self.version).split(".")[0]
         major_compiler_settings_version = compiler_version.split(".")[0]
         if major_version != major_compiler_settings_version:

recipes/arm-gnu-toolchain/all/test_package/CMakeLists.txt

@@ -1,18 +1,19 @@
 cmake_minimum_required(VERSION 3.15)
 
-# This is a workaround for Conan 1.x
-set(CMAKE_TOOLCHAIN_FILE toolchain.cmake)
-
 project(test_package LANGUAGES CXX)
 
-set(test_package_compiler_flags -mcpu=cortex-m0plus
+# Conan's adds host side flags to the conan_toolchain.cmake file which
+# interferes with arm-none-eabi-g++. To fix this, we set CMAKE_CXX_FLAGS
+# to an empty string, then provide target specific flags to the
+# executable.
+set(CMAKE_CXX_FLAGS "")
+
+set(compiler_flags
+  -mcpu=cortex-m0plus
   -mfloat-abi=soft
   --specs=nosys.specs
   --specs=nano.specs)
 
-set(CMAKE_CXX_FLAGS "")
-message(AUTHOR_WARNING "CMAKE_CXX_FLAGS = ${CMAKE_CXX_FLAGS}")
-
 add_executable(${PROJECT_NAME} main.cpp)
-target_compile_options(${PROJECT_NAME} PRIVATE ${test_package_compiler_flags})
-target_link_options(${PROJECT_NAME} PRIVATE ${test_package_compiler_flags})
+target_compile_options(${PROJECT_NAME} PRIVATE ${compiler_flags})
+target_link_options(${PROJECT_NAME} PRIVATE ${compiler_flags})