test: hardcoded ld emulation mode doesn't work on non-darwin env

[folliehiyuki]

https://github.com/thought-machine/please/blob/22137cc3e171d99f9a51df16761f8c8aa1c31359/test/build_defs/cc_embed_binary.build_defs#L67

The build rule hardcodes -m elf_$XARCH argument and passes it to ld.

For my environment (AlpineLinux), this seems to only work on x86_64, and the test //test/cc_rules/gcc:* is failing on AlpineLinux's aarch64 CI: https://gitlab.alpinelinux.org/FollieHiyuki/aports/-/jobs/1049123

[folliehiyuki]

The failed log:

17:10:53.905   ERROR: //test/cc_rules/gcc:_embedded_file_1#lib failed:
Error building target //test/cc_rules/gcc:_embedded_file_1#lib: exit status 1
/usr/bin/ld: unrecognised emulation mode: elf_aarch_64
Supported emulations: aarch64linux aarch64elf aarch64elf32 aarch64elf32b aarch64elfb armelf armelfb aarch64linuxb aarch64linux32 aarch64linux32b armelfb_linux_eabi armelf_linux_eabi
17:10:53.905   ERROR: //test/config_rules:all failed:
None of the select() conditions matched

[stale[bot]]

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