use -std=gnu11 and -std=c++14 for C and C++ flags for all STM32F4 projects.

cmake/gcc_stm32f4.cmake

@@ -1,5 +1,5 @@
-SET(CMAKE_C_FLAGS "-mthumb -fno-builtin -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -Wall -std=gnu99 -ffunction-sections -fdata-sections -fomit-frame-pointer -mabi=aapcs -fno-unroll-loops -ffast-math -ftree-vectorize" CACHE INTERNAL "c compiler flags")
-SET(CMAKE_CXX_FLAGS "-mthumb -fno-builtin -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -Wall -std=c++11 -ffunction-sections -fdata-sections -fomit-frame-pointer -mabi=aapcs -fno-unroll-loops -ffast-math -ftree-vectorize" CACHE INTERNAL "cxx compiler flags")
+SET(CMAKE_C_FLAGS "-mthumb -fno-builtin -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -Wall -std=gnu11 -ffunction-sections -fdata-sections -fomit-frame-pointer -mabi=aapcs -fno-unroll-loops -ffast-math -ftree-vectorize" CACHE INTERNAL "c compiler flags")
+SET(CMAKE_CXX_FLAGS "-mthumb -fno-builtin -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -Wall -std=c++14 -ffunction-sections -fdata-sections -fomit-frame-pointer -mabi=aapcs -fno-unroll-loops -ffast-math -ftree-vectorize" CACHE INTERNAL "cxx compiler flags")
 SET(CMAKE_ASM_FLAGS "-mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -x assembler-with-cpp" CACHE INTERNAL "asm compiler flags")
 
 SET(CMAKE_EXE_LINKER_FLAGS "-Wl,--gc-sections -mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -mabi=aapcs" CACHE INTERNAL "executable linker flags")