Add show_includes GN build argument

Add a show_includes GN build argument which is used for include
file analysis. show_includes requires clang to be used and adds
the -H compile argument. This produces output that can be analyzed
to understand all header files included by the source file being
compiled. Here is a sample of the output:

[11/1330] clang++-14 -H <other-flags...> -c \
  ../../src/gpu/ganesh/GrAHardwareBufferImageGenerator.cpp -o \
. ../../include/core/SkTypes.h
.. ../../include/private/base/SkFeatures.h
.. ../../include/private/base/SkLoadUserConfig.h
... ../../include/private/base/SkFeatures.h
... ../../include/config/SkUserConfig.h
.. ../../include/private/base/SkAPI.h
... ../../include/private/base/SkLoadUserConfig.h

<many other headers>

Bug: skia:12159
Change-Id: Ideeb6daa9fd27cb8f5be02f358b0d1c8c5f6dc91
Auto-Submit: Chris Mumford <>
Reviewed-by: Ben Wagner <>
Reviewed-by: Kevin Lubick <>
Commit-Queue: Chris Mumford <>
2 files changed