Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Replace SOFTFLOAT with __riscv_float_abi_*.

With SOFTFLOAT, libc and libm were built correctly, but any program
including fenv.h itself assumed it was on a hardfloat systen and emitted
inline fpu instructions for fedisableexcept() and friends.

Unlike r315424 which did this for MIPS, I've used riscv_float_abi_soft
and riscv_float_abi_double macros as appropriate rather than using
__riscv_float_abi_soft exclusively. This ensures that attempts to use an
unsupported hardfloat ABI will fail.

Reviewed by: br
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D10039

Correct an misunderstanding of MDSRCS.

MDSRCS it intended to allow assembly versions of funtions with C
implementations listed in MISRCS. The selection of the correct
machdep_ldis?.c for a given architecture does not follow this pattern
and the file should be added to SRCS directly.

Reviewed by: emaste, imp, jhb
MFC after: 1 week
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9841

Add full softfloat and hardfloat support for RISC-V.

Hardfloat is now default (use riscv64sf as TARGET_ARCH
for softfloat).

Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D8529

Bring in initial libc and libstand support for RISC-V.

Reviewed by: andrew, emaste, kib
Sponsored by: DARPA, AFRL
Sponsored by: HEIF5
Differential Revision: https://reviews.freebsd.org/D4943

Start support for the RISC-V 64-bit architecture developed by UC Berkeley.

RISC-V is a new ISA designed to support computer research and education, and
is now become a standard open architecture for industry implementations.

This is a minimal set of changes required to run 'make kernel-toolchain'
using external (GNU) toolchain.

The FreeBSD/RISC-V project home: https://wiki.freebsd.org/riscv.

Reviewed by: andrew, bdrewery, emaste, imp
Sponsored by: DARPA, AFRL
Sponsored by: HEIF5
Differential Revision: https://reviews.freebsd.org/D4445