Convert fs_host files from c back to cpp and style changes.

* fs_darwin.c => fs_darwin.cpp
* fs_freebsd.c => fs_freebsd.cpp
* use bool instead of int again in fs_darwin.cpp (C => C++)
* declare loop varibles inline again in fs_freebsd.cpp (C => C++)
* 2 newlines between top header gaurd and first #include
* 2 newlines after last #include
* freebsd/endian.h and freebsd/regex.h convert \r\n to just \n
* remove some leading tabs in fs_freebsd.cpp
* add newlines after single line if statement in fs_freebsd.cpp
* 80-char limit fixes in fs_freebsd.cpp

Cleanup darwin build system some more.

* Convert fs_darwin.cpp and fs_freebsd.cpp to C.
* Convert extern C calls to __BEGIN_DECLS and __END_DECLS macros
* Link rm_attrs with dynamic libroot

Split fs_darwin.h defines into various platform dependent headers.

This completes the final 1/3 of #8857. Changes again by nielx with
style fixes by me.

The one part that I couldn't figure out, and maybe Ingo can chime
in here. If headers/build/host/darwin/sys/stat.h is surrounded in

extern "C" {

}

guards then I get a link error complaining that the functions defined
here are duplicate symbols, once in fs.o and once in function_remapper.o.
For example:

ld: duplicate symbol _futimens in generated/objects/darwin/x86_64/release/build/libroot/libroot_build_function_remapper.a(function_remapper.o) and generated/objects/darwin/x86_64/release/build/libroot/libroot_build.a(fs.o) for architecture x86_64

I'm not sure why that is.

Convert fs_host files from c back to cpp and style changes.

* fs_darwin.c => fs_darwin.cpp
* fs_freebsd.c => fs_freebsd.cpp
* use bool instead of int again in fs_darwin.cpp (C => C++)
* declare loop varibles inline again in fs_freebsd.cpp (C => C++)
* 2 newlines between top header gaurd and first #include
* 2 newlines after last #include
* freebsd/endian.h and freebsd/regex.h convert \r\n to just \n
* remove some leading tabs in fs_freebsd.cpp
* add newlines after single line if statement in fs_freebsd.cpp
* 80-char limit fixes in fs_freebsd.cpp

Cleanup darwin build system some more.

* Convert fs_darwin.cpp and fs_freebsd.cpp to C.
* Convert extern C calls to __BEGIN_DECLS and __END_DECLS macros
* Link rm_attrs with dynamic libroot

Split fs_darwin.h defines into various platform dependent headers.

This completes the final 1/3 of #8857. Changes again by nielx with
style fixes by me.

The one part that I couldn't figure out, and maybe Ingo can chime
in here. If headers/build/host/darwin/sys/stat.h is surrounded in

extern "C" {

}

guards then I get a link error complaining that the functions defined
here are duplicate symbols, once in fs.o and once in function_remapper.o.
For example:

ld: duplicate symbol _futimens in generated/objects/darwin/x86_64/release/build/libroot/libroot_build_function_remapper.a(function_remapper.o) and generated/objects/darwin/x86_64/release/build/libroot/libroot_build.a(fs.o) for architecture x86_64

I'm not sure why that is.