gcc labels configure test spins forever on armv7, aarch64

[craftyguy]

Using musl libc on Alpine Linux, this configure test seems to spin forever at 100% CPU, using the 20.06.1 src distribution.

gcc is 10.3.1

[wangp]

This should be fixed for aarch64 in ROTDs, though I've personally only tested it with glibc. Aarch64 was not supported as of 20.06.1.

I don't know about armv7. I don't see any changes related to it in the configure script.

[juliensf]

It's possible that the fix applied for aarch64 in commit 4abc9b5 will work for armv7 as well; I don't have access to
a system on which to try it.

At last report, GCC labels were not working correctly on 32-bit ARM, so it may be easiest to simply disable the affected tests in the configuration script, e.g. invoke the configure script as:

     $ mercury_cv_asm_labels=no \
       mercury_cv_gcc_labels=no \
       ./configure

[craftyguy]

Ya as a workaround, I disabled labels for aarch64 and armv7 by patching the configure script (I'm trying to package mercury for Alpine Linux, so carrying that patch is easier)

But, if aarch64 is not supported in 20.06.1, then my efforts are probably in vain.. Any chance there will be a release soon that supports this arch?