[llvm-symbolizer] Add -no-demangle as alias for -demangle=false

Summary: Provides -no-demangle as alias for -demangle=false. Motivation: https://bugs.llvm.org/show_bug.cgi?id=40075

Reviewers: jhenderson, ruiu

Reviewed By: jhenderson

Subscribers: erik.pilkington, rupprecht, llvm-commits

Differential Revision: https://reviews.llvm.org/D56773

llvm-svn: 351735