This make relative pathes shorter an too give a chance to
de-duplicate -isystem flags just like -I flags.
Fix common test case 203 for OSX build host too
It's fairly common on Linux and *BSD platforms to check for these
attributes existence, so it makes sense to me to have this checking
build into meson itself. Autotools also has a builtin for handling
these, and by building them in we can short circuit cases that we know
that these don't exist (MSVC).
Additionally this adds support for two common MSVC __declspec
attributes, dllimport and dllexport. This implements the declspec
version (even though GCC has an __attribute__ version that both it and
clang support), since GCC and Clang support the MSVC version as well.
Thus it seems reasonable to assume that most projects will use the
__declspec version over teh __attribute__ version.
ClausKlein
Wolfgang Stöggl
Michael Hirsch, Ph.D
Jussi Pakkanen
Dylan Baker
Jon Turney
David Seifert