Drop checks for EXTERNAL_TOOLCHAIN for crt*.o. We've been using our own
versions for a long time and haven't relied on external files as such.

branches: 1.11.14;
Make LIBCRT* depend on the right files if MLIBDIR from MKCOMPAT is defined.

branches: 1.10.8;
Add more external dependencies for crtstuff

Revert poor change

Deal with crti and crtn not present in some EXTERNAL_TOOLCHAIN's. Also,
handle "missing" crtstuff internally instead of depending on external
intervention.

unrevert previous. i can't figure out how to make the build break with
the change anymore, so assume it was a sunspot.

revert previous, seems to upset the build in a creative way

Allow user override of _GCC_CRT{BEGIN,END}S.

branches: 1.4.2;
From pooka: Fix EXTERNAL_TOOLCHAIN compilation where crti/crtn are not in the
same directory as crtbegin

branches: 1.3.18;
allow _GCC_*CRT* defines to be overridden in the in-tree toolchain case.

provide a variable pointing to the directory where
the gcc provided crt*.o are located

If EXTERNAL_TOOLCHAIN is defined, allow the compiler to define the
location of crt{begin,end}{,S}.o and libgcc.a. Encapsulate all of
this logic into the new bsd.gcc.mk, and use it in bsd.prog.mk and
bsd.lib.mk.