Source downloads fail

Summary

Running sb-get-sources fails because of incorrect logic in:

1. config/tools/rtems-kernel-common.cfg
2. source-builder/config/glib-2-meson.cfg

The changes are:

-%if %{_dry_run} && %{defined with_download}
+%if %{_dry_run} || %{defined with_download}

GNU GCC git upgrades has broken building gcc-4.9 compilers as the common support contains patches from git. Remove the GCC 4.9 builds from bare.

Changes to fix #9 (closed) in !21 (merged) breaks building RTEMS 7. The MPFR define is not present.

Steps to reproduce

cd rtems
../source-builder/sb-get-sources --stop-on-error