When overriding the CFLAGS variable with a command line argument, all "CFLAGS +=" directives are lost, see
https://www.gnu.org/software/make/manual/html_node/Overriding.html#Overriding
I propose to introduce a new variable GSH_CFLAGS to be changed by the "+=" directive and which is called by COMPILE instead of CFLAGS.
This way make respects the CFLAGS passed by the user.
When overriding the CFLAGS variable with a command line argument, all "CFLAGS +=" directives are lost, see https://www.gnu.org/software/make/manual/html_node/Overriding.html#Overriding I propose to introduce a new variable GSH_CFLAGS to be changed by the "+=" directive and which is called by COMPILE instead of CFLAGS. This way make respects the CFLAGS passed by the user.