[build] Suppress -Wunused-but-set-var in expat

This patch suppresses -Wunused-but-set-variable warning in
expat third party code that does not comply with.

The code that causes the issues is as the following:
third_party/expat/expat/lib/xmlparse.c:709:7: error: variable
'gettimeofday_res' set but not used

Bug: 77973
Change-Id: I8783ca2bd92996bd8d923fa00e28c9e5e3f88610
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/expat/+/550882
Reviewed-by: Tamir Duberstein <tamird@google.com>
1 file changed
tree: 56b583c1088f99d03f6479c16c5341a298478ce7
  1. expat/
  2. htdocs/
  3. testdata/
  4. .gitignore
  5. BUILD.gn
  6. README.fuchsia