Use atomic instructions on ARM linux.

This is safe given how the pre-v6 atomic ops funcions in libgcc are
implemented.

This fixes pr15429.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181728 91177308-0d34-0410-b5e6-96231b3b80d8
Fix a wrong and confusing comment in CharUnits.h. Neither C nor C++ allows
bytes and character units to be different sizes.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181730 91177308-0d34-0410-b5e6-96231b3b80d8
Suppress GCC warning for no return after covered switch, and remove some
debugging code from an unreachable codepath.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181731 91177308-0d34-0410-b5e6-96231b3b80d8
Align a multiline string literal with the first part.

Before:
  #define A(X)          \
    "aaaaa" #X "bbbbbb" \
               "ccccc"

After:
  #define A(X)          \
    "aaaaa" #X "bbbbbb" \
    "ccccc"

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181732 91177308-0d34-0410-b5e6-96231b3b80d8