[ASTMatchers] HasNameMatcher handles `extern "C"`

Summary: Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=42193 | hasName AST matcher is confused by extern "C" in namespace. ]]

Reviewers: klimek, aaron.ballman, gribozavr2

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D75202

(cherry picked from commit 16cabf27)