It's the recommended way to set those, and is more portable
(automatically prepends -D for GCC/Clang and /D for MSVC).
We still use CPPFLAGS for some pre-processor flags which are not
defines.
Include paths are processed from left to right, so we use Prepend to
ensure that paths to bundled thirdparty files will have precedence over
system paths (e.g. `/usr/include` should have lowest priority).
Many contributors (me included) did not fully understand what CCFLAGS,
CXXFLAGS and CPPFLAGS refer to exactly, and were thus not using them
in the way they are intended to be.
As per the SCons manual: https://www.scons.org/doc/HTML/scons-user/apa.html
- CCFLAGS: General options that are passed to the C and C++ compilers.
- CFLAGS: General options that are passed to the C compiler (C only;
not C++).
- CXXFLAGS: General options that are passed to the C++ compiler. By
default, this includes the value of $CCFLAGS, so that setting
$CCFLAGS affects both C and C++ compilation.
- CPPFLAGS: User-specified C preprocessor options. These will be
included in any command that uses the C preprocessor, including not
just compilation of C and C++ source files [...], but also [...]
Fortran [...] and [...] assembly language source file[s].
TL;DR: Compiler options go to CCFLAGS, unless they must be restricted
to either C (CFLAGS) or C++ (CXXFLAGS). Preprocessor defines go to
CPPFLAGS.
- The `cpu-features.{c,h}` code was only used by chance by the webm
(libvpx) code, so I moved it there. It was actually introduced before
that and wasn't in use, and libvpx just happened to be able to
compile thanks to it being bundled.
It could potentially be compiled on the fly from the Android NDK, but
since we plan to replace the webm module by a GDNative plugin in the
near future, I went the bundling route.
- `ifaddrs_android.h` is already provided in the Android NDK as
`ifaddrs.h`, same as on other Unixes. Yet we cannot use it until we
up the min API level to 24, where `getifaddrs` is first defined.
I moved the files to `thirdparty/misc` and synced them with upstream
WebRTC (only indentation changes and removal of `static` qualifiers).
Also removes dropped thirdparty files from COPYRIGHT.txt after changes
in #24105 and #24145.
