Fix CCACHE=sccache with recent sccache versions

[SimonSapin]

Chosen part of the output with sccache 0.2.12:

error: failed to execute compile
caused by: Compiler not supported: "/usr/bin/ar: invalid option -- \'E\'\nUsage: /usr/bin/ar [emulation options] [-]{dmpqrstx}[abcDfilMNoPsSTuvV] [--plugin <name>] [member-name] [count] archive-file file...\n       /usr/bin/ar -M [<mri-script]\n commands:\n  d            - delete file(s) from the archive\n  m[ab]        - move file(s) in the archive\n  p            - print file(s) found in the archive\n  q[f]         - quick append file(s) to the archive\n  r[ab][f][u]  - replace existing or insert new file(s) into the archive\n  s            - act as ranlib\n  t            - display contents of archive\n  x[o]         - extract file(s) from the archive\n command specific modifiers:\n  [a]          - put file(s) after [member-name]\n  [b]          - put file(s) before [member-name] (same as [i])\n  [D]          - use zero for timestamps and uids/gids (default)\n  [U]          - use actual timestamps and uids/gids\n  [N]          - use instance [count] of name\n  [f]          - truncate inserted file names\n  [P]          - use full path names when matching\n  [o]          - preserve original dates\n  [u]          - only replace files that are newer than current archive contents\n generic modifiers:\n  [c]          - do not warn if the library had to be created\n  [s]          - create an archive index (cf. ranlib)\n  [S]          - do not build a symbol table\n  [T]          - make a thin archive\n  [v]          - be verbose\n  [V]          - display the version number\n  @<file>      - read options from <file>\n  --target=BFDNAME - specify the target object format as BFDNAME\n optional:\n  --plugin <p> - load the specified plugin\n emulation options: \n  No emulation specific options\n/usr/bin/ar: supported targets: elf64-x86-64 elf32-i386 elf32-iamcu elf32-x86-64 a.out-i386-linux pei-i386 pei-x86-64 elf64-l1om elf64-k1om elf64-little elf64-big elf32-little elf32-big pe-x86-64 pe-bigobj-x86-64 pe-i386 plugin srec symbolsrec verilog tekhex binary ihex\n"
make[2]: *** [libskia.a] Error 2
make[1]: *** [CMakeFiles/skia.dir/all] Error 2
make: *** [all] Error 2

CC servo/servo#24491

[SimonSapin]

I don’t really understand the issue, but not using sccache for linking seems to fix the issue while keeping most of the benefits of caching during compilation.

[emilio]

Looks good but it seems it may be worth having an upstream issue about this? Specially if it used to work.

[SimonSapin]

On principle yes, but I have no idea how RULE_LAUNCH_LINK, sccache, and /usr/bin/ar all interact together. So it looks like non-trivial investigation would be needed before getting at expected/actual behavior of sccache as appropriate for a bug report :/

[emilio]

After a quick DuckDuckGo search looks like we're not the only ones with this issue: EOSIO/eosio.cdt@d70cfd0

[emilio]

Filed mozilla/sccache#550

[emilio]

ccache seems to just forward everything that doesn't quack as a compiler I guess:

$ ccache echo "foo"
foo

[SimonSapin]

@bors-servo r=emilio

[bors-servo]

📌 Commit 6fbeaf8 has been approved by emilio

[bors-servo]

⌛ Testing commit 6fbeaf8 with merge fe8b4c7...

[bors-servo]

☀️ Test successful - checks-travis
Approved by: emilio
Pushing fe8b4c7 to master...