Disable assembly sources when compiler/assembler cannot compile certain
instructions.

Note this is a direct commit because head and stable/11 has OpenSSL 1.0.2
branch. However, it is based on r304320.

Requested by: julian

- Make libcrypto.so position independent on i386.
- Enable linker error when libcrypto.so contains a relocation against text.
- Add "Do not modify" comment to generated source files.
- Set CC environment variable for Perl scripts to enable AVX instructions.
- Update __FreeBSD_version to indicate libcrypto.so is position independent.

Note this is a direct commit because head has OpenSSL 1.0.2 branch but based
on r299389, r299462, r299464, r299479, and r299480.

MFC r287981:

Replace afterinstall: hack from r111083 with 'make delete-old' functionality.

MFC: r277274

Update buildinf.h to make SSLeay_version(3) little bit more useful.

MFC r287981:

Replace afterinstall: hack from r111083 with 'make delete-old' functionality.

MFC: r277274

Update buildinf.h to make SSLeay_version(3) little bit more useful.