BaseTools/GccBase.lds: don't copy RELA section to PE/COFF
The CLANG38 toolchain creates a PIE binary at link time. This is
necessary since the LTO code generation may otherwise result in
code that cannot execute correctly when loaded above 2 GB.
PIE executables contain a RELA section consisting of dynamic
relocation entries that are intended for consumption by the loader
at runtime. For this reason, it has the SHF_ALLOC attribute set by
default, and will be identified by GenFw as a section that needs to
be copied into the PE/COFF binary, resulting in waste of space since
the PE/COFF loader does not use this data at all.
So mark the RELA section as informational: this will prevent the
linker from setting the SHF_ALLOC attribute, causing GenFw to
ignore it.