'-w' in c_command will check for it as a substring, which will also
match '-wd', etc. So match it with quotes. This won't give us false
positives, but might give us false negatives in case the argument is not
quoted, but that's better behaviour for a test.
The alternative is to split the string command, but the command does not
necessarily obey shell quoting rules, so we cannot reliably use
shlex.split().
This approach is locale-independent and more correct. For instance, this
will work with UTF-16 while the previous approach with binary comparison
would not.
This also removes the need for doing an explicit decode to utf-8 which
is lossy and can fail by yielding no output at all.
We want compiler check arguments (-O0, -fpermissive, etc) to override
all other arguments, and we want extra_args passed in by the build file
to always override everything.
To do this properly, we must split include arguments out, append them
first, append all other arguments as usual, and then append the rest.
As part of this, we also add the compiler check flags to the
cc.compiles() and cc.links() helper functions since they also most
likely need them.
Also includes a unit test for all this.
This can only be done as a unit test because it requires changes to the
environment. This also means we need to pass the current environment to
subprocess.check_output, which we should always do anyway since the
environment is torn down and restored between each test.
Nirbheek Chauhan
Jussi Pakkanen
Igor Gnatenko
Elliott Sales de Andrade