[lit, pdb] Fix func-symbols.test (on Windows)

Summary: This test was failing sporadically on windows because the order in which the symbols are generated was different between builds. To fix the test, we need to run FileCheck twice - once for each set of symbols we want to verify. The test only runs on Windows.

Reviewers: asmith, zturner, labath

Subscribers: stella.stamenova, llvm-commits

Differential Revision: https://reviews.llvm.org/D47746

llvm-svn: 334025