Doing so prevents -m32/-m64 from having any effect.  This patch is just
a workaround; we should fix the runtime handling of --with-arch so that
specifying -m32/-m64 on the command line takes priority.

When a function clobbers only s0 and s1, but not ra, we don't want to use
the save/restore routines because the stack would grow more than needed.

Make GCC pass through non-standard ISA strings

This simply stops GCC's parse whenever it sees an 'X' in an ISA
string.  This is the best I can do until some clarafications are made
to the RISC-V user spec that allows ISA extensions to be parsed.

These call library routines to save and restore the callee-saved registers
and link register.

Fix some glibc FP routines for non-F

Some glibc floating point routines use inline assembly.  This changes
them to use regular C code to do this when compiled without hardware
floatint-point support.  The change just uses regular C to perform
these operations when compiled on ABIs without hardware floating
point.

It's DISTDIR, not DESTDIR

$ grep DISTDIR Makefile.in
DISTDIR ?= /var/cache/distfiles

h/t Larry Doolittle

Imafd not g

G doesn't actually work.

--with-arch

This matches the GCC configure option.

Add "--with-base-isa" to configure

Allow newlib to build without F

This allows someone to build a RV32I toolchain without going in and
messing with the Makefile directly.

GCC's softfloat is built by default without support for dynamic
rounding modes.  This makes softfloat newlib's floating point always
round-to-zero, and returns a failure code when trying to set it.

This patch is needed to make newlib compile on anything without F, as
it used to try use an undefined instruction to do this.

You're only supposed to return 0 if the exception mask was set
correctly, and this doesn't set the mask at all.

It was happening too late, which overrode the -m32/-m64 flags.

binutils: gas: fix default xlen selection

gas currently defaults to xlen=64 all the time even when it's configured
for a riscv32-elf target.  Fix this by leveraging the existing default
arch logic like x86/s390 targets do.

The meaning of "arch" is a bit confusing in this case as we're using it
only for the xlen and not for the various extensions.  But since this is
really the only thing we pull from the tuple, and it's the naming that
the common gas code uses, oh well.

disassembler fixes

libiberty provides memory helpers to handle error conditions for free.

There are times when the disassembler doesn't have a fully formed elf
(like when using gdb).  Change the extension logic to not require that
so we don't crash with segfaults.