Add HLSL debug metadata emission for DXIL by embedding non-system source
files (including included headers) into dx.source.contents, recording
the main file name and user defines, and serializing the dxc-style
command line into dx.source.args.
These metadata nodes are needed for emitting SRCI part of a debug
DXContainer in llc.
Introduce -fdx-record-command-line option to cc1 to carry the escaped
dxc driver command line into cc1.
Introduce -fdx-no-source-metadata CodeGen option to cc1, to be able to
disable dx.source metadata nodes emission. This comes in handy for
writing debug info tests, so that CHECK-NOT lines do not match
themselves in LLVM IR. For example, without this option, in
`clang/test/CodeGenHLSL/debug/source-language.hlsl`, CHECK-V4-NOT line
gets a match on the line with dx.source.contents node.
Vladislav Dzhidzhoev
63c9264c77