Remove usage of CMAKE_<LANG>_FLAGS_<CONFIG>_INIT CMake variables.

As they were introduced in CMake 3.11, and this project currently
support 3.6+.

The CMAKE_<LANG>_FLAGS_<CONFIG> are reset here instead of using
_INIT, as we want these to be the starting values, overwritting
any CMake defaults.

Author: microbit-carlos

utils/cmake/toolchains/ARM_GCC/compiler-flags.cmake

@@ -31,33 +31,30 @@ set(CMAKE_DEPFILE_FLAGS_CXX "-MMD -MT <OBJECT> -MF <DEPFILE>")
 set(CMAKE_C_OUTPUT_EXTENSION ".o")
 set(CMAKE_DEPFILE_FLAGS_C "-MMD -MT <OBJECT> -MF <DEPFILE>")
 
-set(CMAKE_C_FLAGS_RELWITHDEBINFO      "-g ${DWARF_VERSION_FLAG}")
 set(CMAKE_C_FLAGS_DEBUG_INIT          "-g ${DWARF_VERSION_FLAG}")
 set(CMAKE_C_FLAGS_MINSIZEREL_INIT     "-Os -DNDEBUG")
 set(CMAKE_C_FLAGS_RELEASE_INIT        "-Os -DNDEBUG")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-Os -g ${DWARF_VERSION_FLAG} -DNDEBUG")
+set(CMAKE_C_FLAGS_RELWITHDEBINFO      "-Os -DNDEBUG -g ${DWARF_VERSION_FLAG}")
 set(CMAKE_INCLUDE_SYSTEM_FLAG_C "-isystem ")
 
-set(CMAKE_ASM_FLAGS_RELWITHDEBINFO      "-g ${DWARF_VERSION_FLAG}")
-set(CMAKE_ASM_FLAGS_DEBUG_INIT          "-g ${DWARF_VERSION_FLAG}")
+set(CMAKE_ASM_FLAGS_DEBUG               "-g ${DWARF_VERSION_FLAG}")
 set(CMAKE_ASM_FLAGS_MINSIZEREL_INIT     "-Os -DNDEBUG")
 set(CMAKE_ASM_FLAGS_RELEASE_INIT        "-Os -DNDEBUG")
-set(CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT "-Os -g ${DWARF_VERSION_FLAG} -DNDEBUG")
+set(CMAKE_ASM_FLAGS_RELWITHDEBINFO      "-Os -DNDEBUG -g ${DWARF_VERSION_FLAG}")
 set(CMAKE_INCLUDE_SYSTEM_FLAG_ASM  "-isystem ")
 
 set(CMAKE_CXX_CREATE_STATIC_LIBRARY "<CMAKE_AR> -cr <LINK_FLAGS> <TARGET> <OBJECTS>")
 
 set(CMAKE_CXX_LINK_EXECUTABLE       "<CMAKE_CXX_COMPILER> <CMAKE_CXX_LINK_FLAGS> <LINK_FLAGS> -Wl,-Map,<TARGET>.map -Wl,--start-group <OBJECTS> <LINK_LIBRARIES> -lnosys -lstdc++ -lsupc++ -lm -lc -lgcc -lstdc++ -lsupc++ -lm -lc -lgcc -Wl,--end-group  --specs=nano.specs -o <TARGET>")
 
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO      "-g ${DWARF_VERSION_FLAG}")
-set(CMAKE_CXX_FLAGS_DEBUG_INIT          "-g ${DWARF_VERSION_FLAG}")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT     "-Os -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT        "-Os -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-Os -g ${DWARF_VERSION_FLAG} -DNDEBUG")
+set(CMAKE_CXX_FLAGS_DEBUG               "-g ${DWARF_VERSION_FLAG}")
+set(CMAKE_CXX_FLAGS_MINSIZEREL          "-Os -DNDEBUG")
+set(CMAKE_CXX_FLAGS_RELEASE             "-Os -DNDEBUG")
+set(CMAKE_CXX_FLAGS_RELWITHDEBINFO      "-Os -DNDEBUG -g ${DWARF_VERSION_FLAG}")
 set(CMAKE_INCLUDE_SYSTEM_FLAG_CXX "-isystem ")
 
 if (CMAKE_C_COMPILER_VERSION VERSION_GREATER "7.1.0" OR CMAKE_C_COMPILER_VERSION VERSION_EQUAL "7.1.0")
     message("${BoldRed}Supressing -Wexpansion-to-defined.${ColourReset}")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-expansion-to-defined")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-expansion-to-defined")
-endif ()
+endif ()

utils/cmake/toolchains/AVR_GCC/compiler-flags.cmake

@@ -1,3 +1,6 @@
+# This file is using CMAKE_<LANG>_FLAGS_<CONFIG>_INIT introduced in 3.11
+cmake_minimum_required(VERSION 3.11)
+
 set(EXPLICIT_INCLUDES "")
 if((CMAKE_VERSION VERSION_GREATER "3.4.0") OR (CMAKE_VERSION VERSION_EQUAL "3.4.0"))
     # from CMake 3.4 <INCLUDES> are separate to <FLAGS> in the

utils/cmake/toolchains/XTENSA_GCC/compiler-flags.cmake

@@ -1,3 +1,6 @@
+# This file is using CMAKE_<LANG>_FLAGS_<CONFIG>_INIT introduced in 3.11
+cmake_minimum_required(VERSION 3.11)
+
 set(EXPLICIT_INCLUDES "")
 if((CMAKE_VERSION VERSION_GREATER "3.4.0") OR (CMAKE_VERSION VERSION_EQUAL "3.4.0"))
     # from CMake 3.4 <INCLUDES> are separate to <FLAGS> in the