Roll wasi-libc to include snapshot1 (#84)

This brings in the following changes:

f645f49 Update signal macros after upgrade to snapshot1 (#144)
8b3266d github actions: pin checkout action to v1 (#145)
410c660 Use constructor functions for optional init routines. (#142)
fe13053 c header generation updated for reorganized witx ast (#139)
cd74e1d Correct the version of #136 on master (#141)
446cb3f Wasi snapshot preview1 (#140)
54102f0 Ignore rights in libpreopen. (#129)
8c9e1c6 Make the `__original_main` definition weak, fixing -flto. (#138)
cf81683 Optimize `fmin`, `fmax`, etc. (#120)
deb8eae Don't pre-check capabilities in `openat`. (#130)
ca9046d Use consistent style for wasi-libc C source files. (#131)
951cc3e Fix unintended recursion in __wasilibc_register_preopened_fd. (#133)
5216983 Avoid a `strdup` call in `__wasilibc_populate_libpreopen`. (#128)
70099d4 Don't link in libpreopen initialization code when it isn't needed. (#127)
ec4549d Temporarily disable the use of `__heap_base`. (#132)
a214f1c Use __heap_base by dlmalloc (#114)
a94d2d0 Avoid varargs conventions when calling open (#126)
7fcc4f2 Revamp and simplify the libpreopen code. (#110)
eb7230c Remove more unsupported headers. (#123)