Respect user-set compiler and linker flags

[AMDmi3]

No description provided.

[greno4ka]

This is really good idea! For example, I want to compile your program on my Android phone, using clang.

Please, merge this PR to your project!

[mpereira]

CC ?= gcc seems to not set the CC variable if the CC environment variable is unset in the shell.

Should this be handled with make conditional expressions instead?

[mpereira]

cc @greno4ka

[AMDmi3]

CC ?= gcc seems to not set the CC variable if the CC environment variable is unset in the shell.

No, it does. It may be affected by the system rules though which may set other default values.

% cat Makefile 
CC ?= gcc
CXX ?= g++
FOO ?= foo
  
all:
	@echo CC=${CC}
	@echo CXX=${CXX}
	@echo FOO=${FOO}
% make       
CC=cc
CXX=g++
FOO=foo
% CC=clang CXX=clang++ FOO=bar make
CC=clang
CXX=clang++
FOO=bar

[greno4ka]

I think @AMDmi3 is right. I saw many opensource projects, where is used "?=". I vote for merging this commit. How else can I help?

[mpereira]

Thanks for the quick replies @AMDmi3 @greno4ka

What I meant was this:

$ cat Makefile
CC ?= gcc
CXX ?= g++
FOO ?= foo

all:
	@echo CC=${CC}
	@echo CXX=${CXX}
	@echo FOO=${FOO}
$ make
CC=cc
CXX=c++
FOO=foo
$ export CC=
$ make
CC=
CXX=c++
FOO=foo

If you think this is fine I'll merge it.

[mpereira]

Thanks @AMDmi3!