Test case tls-gd-mcmodel-large passes invalid compile-flag combination to gcc on aarch64

[sicherha]

When building mold 1.1.1 for Fedora on aarch64, the tls-gd-mcmodel-large test case fails because GCC does not support the combination of -mcmodel=large with -fPIC. This is documented here: https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html

Output of instrumented test case:

++ basename ./elf/tls-gd-mcmodel-large.sh .sh
+ testname=tls-gd-mcmodel-large
Testing tls-gd-mcmodel-large ... + echo -n 'Testing tls-gd-mcmodel-large ... '
++ dirname ./elf/tls-gd-mcmodel-large.sh
+ cd ./elf/../..
++ pwd
+ mold=/builddir/build/BUILD/mold-1.1.1/mold
+ t=out/test/elf/tls-gd-mcmodel-large
+ mkdir -p out/test/elf/tls-gd-mcmodel-large
++ uname -m
+ '[' aarch64 = x86_64 ']'
++ uname -m
+ '[' aarch64 = aarch64 ']'
+ dialect=trad
+ cat
+ gcc -mtls-dialect=trad -fPIC -c -o out/test/elf/tls-gd-mcmodel-large/a.o -xc - -mcmodel=large
cc1: sorry, unimplemented: code model 'large' with '-fPIC'

I tried replacing gcc with clang as a quick fix, but Clang doesn't know the -mtls-dialect=gnu option.

Curiously, the test case contains an explicit if-branch for setting the correct TLS dialect on aarch64. Does this mean that it worked at some point in the past? The sentence

The -mcmodel=large option is incompatible with -mabi=ilp32, -fpic and -fPIC.

was added in the documentation for GCC 10; it was not yet present in the GCC 9 documentation.

[sicherha]

Same thing for tls-ld-mcmodel-large.

Related pull request: #286