Fixes part of issue #14921.

When $(FPIC) gets added to TARGET_CFLAGS (for instance), we can
count on $(TARGET_CFLAGS) in turn being quoted when it gets
expanded.  But there are a few places where $(FPIC) gets
expanded directly into environment variables passed on the
command line, such as when setting lt_cv_* variables as in this
case.

It's wrong to assume that the expansion of $(FPIC) won't require
quoting (such as it containing spaces) if it has multiple compiler
flags.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>