Added C standard gnu23 to the makefile (#288)

* Added C standard gnu23 to the makefile

* Added gnu23 standard to all test modue makefiles

* Added installation of latest gcc version to tests workflow

* Fixed typo in previous commit

* Made GCC 14 installation conditional and moved from the workflow to the script

* Extracted GCC version check to external script for CI and created tests README

* Added #!/bin/bash

* Make check_gcc_version.sh executable

Makefile

@@ -42,7 +42,7 @@ GIT_DIRTY := $(shell git diff-index --quiet HEAD -- || echo "-dirty")
 GIT_HASH := $(shell git rev-parse --short HEAD || echo "undef")
 GIT_C_FLAGS := -DGIT_HASH=\"$(GIT_HASH)\" -DGIT_DIRTY=\"$(GIT_DIRTY)\"
 
-CFLAGS	:= -g -O3 -Wall -Werror \
+CFLAGS	:= -g -O3 -Wall -Werror -std=gnu23 \
         -mcpu=arm7tdmi -mtune=arm7tdmi \
         -ffast-math -fomit-frame-pointer -funroll-loops \
         $(ARCH)