Hi Rich,
I have attached the patch which has all the MIPS n64 porting work. I have created mipsn64port_review remote branch on GitHub and please have a look at
https://github.com/MaheshBodapati/musl/commits/mipsn64port_review  which has the broken down patches and the base revision on which we have prepared patch is d150764

We have tested on both little endian and big endian, here are the FAILS

Musl mips n64 libc testing on EL :

Fails: 17
FAIL ./src/api/main.exe [status 1]
FAIL ./src/functional/wcstol-static.exe [status 1]
FAIL ./src/functional/wcstol.exe [status 1]
FAIL ./src/math/acosh.exe [status 1]
FAIL ./src/math/asinh.exe [status 1]
FAIL ./src/math/j0.exe [status 1]
FAIL ./src/math/jn.exe [status 1]
FAIL ./src/math/jnf.exe [status 1]
FAIL ./src/math/lgamma.exe [status 1]
FAIL ./src/math/lgamma_r.exe [status 1]
FAIL ./src/math/lgammaf.exe [status 1]
FAIL ./src/math/lgammaf_r.exe [status 1]
FAIL ./src/math/sinh.exe [status 1]
FAIL ./src/math/tgamma.exe [status 1]
FAIL ./src/math/y0.exe [status 1]
FAIL ./src/math/y0f.exe [status 1]
FAIL ./src/math/ynf.exe [status 1]

Musl mips n64 libc testing on EB :
Fails:17
FAIL ./src/api/main.exe [status 1]
FAIL ./src/functional/wcstol-static.exe [status 1]
FAIL ./src/functional/wcstol.exe [status 1]
FAIL ./src/math/acosh.exe [status 1]
FAIL ./src/math/asinh.exe [status 1]
FAIL ./src/math/j0.exe [status 1]
FAIL ./src/math/jn.exe [status 1]
FAIL ./src/math/jnf.exe [status 1]
FAIL ./src/math/lgamma.exe [status 1]
FAIL ./src/math/lgamma_r.exe [status 1]
FAIL ./src/math/lgammaf.exe [status 1]
FAIL ./src/math/lgammaf_r.exe [status 1]
FAIL ./src/math/sinh.exe [status 1]
FAIL ./src/math/tgamma.exe [status 1]
FAIL ./src/math/y0.exe [status 1]
FAIL ./src/math/y0f.exe [status 1]
FAIL ./src/math/ynf.exe [status 1]


Thanks,
Mahesh