superh port
make the x32 port use the correct ld-musl-x32.path filename

previously it was wrongly using the x86_64 one, precluding having both
x32 and x86_64 libs present on the same system.
fixup general __syscall breakage introduced in x32 port

the reordering of headers caused some risc archs to not see
the __syscall declaration anymore.
this caused build errors on mips with any compiler,
and on arm and microblaze with clang.

we now declare it locally just like the powerpc port does.
mips: add mips-sf subarch support (soft-float)

Userspace emulated floating-point (gcc -msoft-float) is not compatible
with the default mips abi (assumes an FPU or in kernel emulation of it).
Soft vs hard float abi should not be mixed, __mips_soft_float is checked
in musl's configure script and there is no runtime check. The -sf subarch
does not save/restore floating-point registers in setjmp/longjmp and only
provides dummy fenv implementation.
add missing sub files for mipsel-sf to use softfloat code

the build system has no automatic way to know this code applies to
both big (default) and little endian variants, so explicit .sub files
are needed.
elf.h: new elf header flag to mark 2008-NaN vs legacy-NaN on mips

see glibc commit 9c21573c02446b3d5cf6a34b67c8545e5be6a600
elf.h: add aarch64 relocations
sys/socket.h: add the SO_MAX_PACING_RATE SOL_SOCKET option

introduced in linux v3.13, 62748f32d501f5d3712a7c372bbb92abc7c62bc7
if_ether.h: new ethernet protocol type

for High-availability Seamless Redundancy (HSR) specified in IEC 62439-3
new in linux v3.13, f421436a591d34fa5279b54a96ac07d70250cc8d
in.h: new IP_MTU_DISCOVER mode IP_PMTUDISC_INTERFACE

introduced in linux v3.13, 482fc6094afad572a4ea1fd722e7b11ca72022a0
to mitigate dns cache poisoning via fragmentation