Remove all invocations of SetSubDirSupportedPlatformsBeOSCompatible.

Use libstdc++, libsupc++ and libgcc from gcc_syslibs.

* Instead of faking libstdc++.so from libstdc++.a, use libstdc++.so
from the gcc_syslibs build feature for everything except x86_gcc2.
* Use libgcc_s.so from the gcc_syslibs build feature for everything but
x86_gcc2 (which still carries libgcc as part of libroot.so).
* Drop filtering of libgcc objects for libroot, as that is no longer
necessary since we're only using libgcc-as-single-object for libroot
with x86_gcc2, where the filtered object file doesn't exist. Should
the objects that used to be filtered cause any problems as part of
libgcc_s.so, we can always filter them as part of the gcc build.
* Use libsupc++.so from the gcc_syslibs build feature for everything but
x86_gcc2.
* Adjust all Jamfiles accordingly.
* Deactivate building of faked libstdc++.so for non-x86-gcc2. For
x86_gcc2, we still build libstdc++.so from the sources in the Haiku
source tree as part of the Haiku build .
* Put gcc_syslibs package onto the image, when needed.

Added a test to compare various header parsers.

* HaikuMailFormatFilter is using the new extract_from_header() method
to retrieve its fields, but that one is often rather slow in comparison.
* Added a test parse_fields() method that outperforms it considerably.

Use libstdc++, libsupc++ and libgcc from gcc_syslibs.

* Instead of faking libstdc++.so from libstdc++.a, use libstdc++.so
from the gcc_syslibs build feature for everything except x86_gcc2.
* Use libgcc_s.so from the gcc_syslibs build feature for everything but
x86_gcc2 (which still carries libgcc as part of libroot.so).
* Drop filtering of libgcc objects for libroot, as that is no longer
necessary since we're only using libgcc-as-single-object for libroot
with x86_gcc2, where the filtered object file doesn't exist. Should
the objects that used to be filtered cause any problems as part of
libgcc_s.so, we can always filter them as part of the gcc build.
* Use libsupc++.so from the gcc_syslibs build feature for everything but
x86_gcc2.
* Adjust all Jamfiles accordingly.
* Deactivate building of faked libstdc++.so for non-x86-gcc2. For
x86_gcc2, we still build libstdc++.so from the sources in the Haiku
source tree as part of the Haiku build .
* Put gcc_syslibs package onto the image, when needed.

Added a test to compare various header parsers.

* HaikuMailFormatFilter is using the new extract_from_header() method
to retrieve its fields, but that one is often rather slow in comparison.
* Added a test parse_fields() method that outperforms it considerably.