[dmd-cxx] Synchronize extern(C) bindings

[ibuclaw]

Only parts of note are Musl and Darwin mach.loader.

[dlang-bot]

Thanks for your pull request, @ibuclaw!

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Testing this PR locally

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dub fetch digger
dub run digger -- build "dmd-cxx + druntime#2741"

[ibuclaw]

@Geod24 - rebased.

[Geod24]

LGTM, no merge right tho.

[ibuclaw]

@Geod24 - Oh well... :-)

[Geod24]

@ibuclaw : So, backtrace & co are not part of Musl, and I doubt they'll get integrated.
On Alpine, libexecinfo provides those symbols. Is there a good way to express this ? In my packages I just link libexecinfo, but open to suggestions.

[ibuclaw]

@Geod24 - In my build, I can see that gcc's in-tree libbacktrace is built, and I can't see it disabled from the system installed gcc either, so I don't think that's a problem.

Configured with: /home/buildozer/aports/main/gcc/src/gcc-8.3.0/configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --build=x86_64-alpine-linux-musl --host=x86_64-alpine-linux-musl --target=x86_64-alpine-linux-musl --with-pkgversion='Alpine 8.3.0' --enable-checking=release --disable-fixed-point --disable-libstdcxx-pch --disable-multilib --disable-nls --disable-werror --disable-symvers --enable-__cxa_atexit --enable-default-pie --enable-default-ssp --enable-cloog-backend --enable-languages=c,c++,objc,fortran,ada --disable-libssp --disable-libmpx --disable-libmudflap --disable-libsanitizer --enable-shared --enable-threads --enable-tls --with-system-zlib --with-linker-hash-style=gnu