Rollup of fixes since the 9.0.0 release.

• Change the default -march for i386 from i486 to i586. This avoids the need for libatomics and had been the defacto default for some time. [0]

• Add -m(no)-spe to clang. (powerpc)

• Deduce MIPS specific ELF header flags from emulation. (mips)

• Fix a variety of assertions and compile/link errors including crashes with CPUTYPE=haswell. [1]

• Switch back to https for downloads. [2]

The new patches were initially committed to FreeBSD src by dim@.

PR: 240918 [0], 240759 [1], 240870 [2]
Reported by: jbeich [0,1], Miyashita Touka <imagin8r@protonmail.com> [2]