Sync the aarch64-vx7r2 libgcc config with that of Linux

Sync the aarch64-vx7r2 libgcc config with that of Linux

This adds ${cpu_type}/t-lse and t-slibgcc-libgcc to the tmake_file
list for aarch64-vxworks7* configurations, as the Linux port does.

t-lse is needed by all triplets now anyway and the standard setting
for slibgcc makes sense as we are working on reintroducing PIC support
for RTPs on various targets. The VxWorks7 system environments are leaning
towards more and more similarilties with Linux in general, so the
closer configurations the better.

2020-11-02  Pat Bernardi  <bernardi@adacore.com>

libgcc/
	* config.host (aarch64-vxworks7*, tmake_file): Add
	${cpu_type}/t-lse and t-slibgcc-libgcc.

Co-authored-by: Olivier Hainque  <hainque@adacore.com>