DataFlowSanitizer: Add a debugging feature to help us track nonzero labels.

Summary:
When the -dfsan-debug-nonzero-labels parameter is supplied, the code
is instrumented such that when a call parameter, return value or load
produces a nonzero label, the function __dfsan_nonzero_label is called.
The idea is that a debugger breakpoint can be set on this function
in a nominally label-free program to help identify any bugs in the
instrumentation pass causing labels to be introduced.

Reviewers: eugenis

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1405

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188472 91177308-0d34-0410-b5e6-96231b3b80d8
Use a reference instead of making an unnecessary copy. Also use 'const'.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188483 91177308-0d34-0410-b5e6-96231b3b80d8
Make a few more things const.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188484 91177308-0d34-0410-b5e6-96231b3b80d8
make arm-reserve-r9 available for all ARM

r9 is defined as a platform-specific register in the ARM EABI.
It can be reserved for a special purpose or be used as a general
purpose register. Add support for reserving r9 for all ARM, while
leaving the IOS usage unchanged.

Patch by Jeroen Hofstee.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188485 91177308-0d34-0410-b5e6-96231b3b80d8
make arm-use-movt available for all ARM

Before this patch this flag is IOS specific, but is also
useful for bare project like bootloaders / kernels etc,
since movw / movt prevents simple relocation. Therefore
make this flag more commonly available.

note: this patch depends on a similiar rename in clang

Patch by Jeroen Hofstee.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188487 91177308-0d34-0410-b5e6-96231b3b80d8
Fixing a corner-case bug in strchr and strrchr lib call optimizations where
the input character is not converted to char before comparing with zero.

The patch was discussed in this thread:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20130812/184069.html

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188489 91177308-0d34-0410-b5e6-96231b3b80d8