driver: pass '-fPIC' option to assembler as well

Summary:
Before the patch '-fPIC' was passed only to C compiler,
but not to assembler itself.

It led to runtime crash in GHC_DYNAMIC_PROGRAMS=YES mode
on sparc32.

Technical details are in 'Note [-fPIC for assembler]'.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Test Plan: validate on sparc

Reviewers: simonmar, austin, kgardas

Reviewed By: austin

Subscribers: simonmar, ezyang, carter

Differential Revision: https://phabricator.haskell.org/D177
Revert "disable shared libs on sparc (linux/solaris) (fixes #8857)"

This reverts commit 623883f1ed0ee11cc925c4590fb09565403fd231.

The commit a93ab43ab5f40cadbedea2f6342b93c245e91434
    driver: pass '-fPIC' option to assembler as well
fixes shared libraries on sparc at least on linux.

Properly fixes Issue #8857

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>