commit ae9ac2a1 from !165 introduced a regression when
fontconfig is built as a subproject. In that case we
would fail to correctly construct the path to the root
build dir where the meson-info subdirectory resides,
instead looking for it in the fontconfig subproject
subdir. This would result in
FAILED: subprojects/fontconfig/src/fcobjshash.gperf
errors in the cutout.py script.
Instead use the @BUILD_ROOT@ substitution to get
to the build root which will work correctly in
either scenario.
Pass c_args to the compiler when preprocessing the gperf header file,
they might contain important bits without which compilation/preprocessing
might fail (e.g. with clang on Android). cc.cmd_array() does not include
the c_args and we can't easily look them up from the meson.build file, so
we have to retrieve from the introspection info.
This is basically the Meson equivalent to commit 57103773.
Instead, when building with Visual Studio-style compilers, define 'FcPublic' as
appropriate so that symbols will be exported without the need to maintain a
.def file.