[Clang] Reset FP options before function instantiations

This is recommit of 98390ccb, reverted
in 82a3969d, because it caused
https://github.com/llvm/llvm-project/issues/63542. Although the problem
described in the issue is independent of the reverted patch, fail of
PCH/late-parsed-instantiations.cpp indeed obseved on PowerPC and is
likely to be caused by wrong serialization of `LateParsedTemplate`
objects. In this patch the serialization is fixed.

Original commit message is below.

Previously function template instantiations occurred with FP options
that were in effect at the end of translation unit. It was a problem
for late template parsing as these FP options were used as attributes of
AST nodes and may result in crash. To fix it FP options are set to the
state of the point of template definition.

Differential Revision: https://reviews.llvm.org/D143241