[clang-tidy] Add non-inline function definition and variable definition check in header files.

Summary: The new check will find all functionand variable definitions which may violate cpp one definition rule in header file.

Reviewers: aaron.ballman, alexfh

Subscribers: aaron.ballman, cfe-commits

Patch by Haojian Wu!

Differential Revision: http://reviews.llvm.org/D15710

llvm-svn: 257178