selftests/nolibc: run-tests.sh: enable testing via qemu-user

qemu-user is faster than a full system test.

Link: https://lore.kernel.org/r/20770915-nolibc-run-user-v1-2-3caec61726dc@weissschuh.net
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

selftests/nolibc: add configuration for mipso32be

Allow testing MIPS O32 big endian.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>

selftests/nolibc: use XARCH for MIPS

MIPS has many different configurations prepare the support of additional
ones by moving the build of MIPS to the generic XARCH infrastructure.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>

selftests/nolibc: add script to run testsuite

The script can run the testsuite for multiple architectures and provides
an overall test report.

Furthermore it can automatically download crosstools from
mirrors.kernel.org if requested by the user.

Example execution:

$ ./run-tests.sh
i386: 162 test(s): 162 passed, 0 skipped, 0 failed => status: success
x86_64: 162 test(s): 162 passed, 0 skipped, 0 failed => status: success
arm64: 162 test(s): 162 passed, 0 skipped, 0 failed => status: success
arm: 162 test(s): 162 passed, 0 skipped, 0 failed => status: success
mips: 162 test(s): 161 passed, 1 skipped, 0 failed => status: warning
ppc: 162 test(s): 162 passed, 0 skipped, 0 failed => status: success
ppc64: 162 test(s): 162 passed, 0 skipped, 0 failed => status: success
ppc64le: 162 test(s): 162 passed, 0 skipped, 0 failed => status: success
riscv: 162 test(s): 162 passed, 0 skipped, 0 failed => status: success
s390: 162 test(s): 161 passed, 1 skipped, 0 failed => status: warning
loongarch: 162 test(s): 161 passed, 1 skipped, 0 failed => status: warning

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20231105-nolibc-run-tests-v1-1-b59ff770a978@weissschuh.net