Workaround for g++ and glibc that define `minor` in `<sys/types.h>`.

Building prjxray using g++ 7.3.0 and glibc 2.27-3 produces the following warning that is treated as an error:

    In file included from [...]/prjxray/lib/include/prjxray/xilinx/xc7series/configuration_column.h:8:0,
                     from [...]/prjxray/lib/include/prjxray/xilinx/xc7series/configuration_bus.h:10,
                     from [...]/prjxray/lib/xilinx/xc7series/configuration_bus.cc:1:
    [...]/prjxray/lib/include/prjxray/xilinx/xc7series/frame_address.h:32:13: error: In the GNU C Library, "minor" is defined
     by <sys/sysmacros.h>. For historical compatibility, it is
     currently defined by <sys/types.h> as well, but we plan to
     remove this soon. To use "minor", include <sys/sysmacros.h>
     directly. If you did not intend to use a system-defined macro
     "minor", you should undefine it after including <sys/types.h>. [-Werror]
      uint8_t minor() const;
                 ^~~~~~~~~~~

This is related to these two bugs:

https://sourceware.org/bugzilla/show_bug.cgi?format=multiple&id=19239

https://bugzilla.redhat.com/show_bug.cgi?id=130601

This patch is a workaround that undefines `minor` if `_GNU_SOURCE` is defined.

Signed-off-by: Christian Fibich <fibich@technikum-wien.at>

lib/include/prjxray/xilinx/xc7series/frame_address.h

@@ -7,6 +7,10 @@
 #include <prjxray/xilinx/xc7series/block_type.h>
 #include <yaml-cpp/yaml.h>
 
+#ifdef _GNU_SOURCE
+#undef minor
+#endif
+
 namespace prjxray {
 namespace xilinx {
 namespace xc7series {