deadlock when zig test -lc is run simultaneously with zig run -lc

[FireFox317]

This came up when trying to hookup the new LLVM backend of the self-hosted compiler to the test-stage2.

The tests runner of the CBE calls zig run -lc on the c code to execute it, however the tests are already executed with zig test <etc> -lc which causes a deadlock in glibc.buildSharedObjects:

0x00007ffff7acb46b in flock () from /usr/lib/libc.so.6
(gdb) bt
#0  0x00007ffff7acb46b in flock () from /usr/lib/libc.so.6
#1  0x0000555556663a7f in std.os.flock (fd=8, operation=2)
    at /home/timon/dev/zig/zig-source/lib/std/os.zig:4099
#2  0x00005555564cbfdb in std.fs.Dir.openFileZ (self=..., 
    sub_path=0x7fffffff4990 "23fa09cb6f3a41d48e130d0e1309e089.txt", flags=...)
    at /home/timon/dev/zig/zig-source/lib/std/fs.zig:768
#3  0x00005555564c6420 in std.fs.Dir.openFile (self=..., sub_path=..., flags=...)
    at /home/timon/dev/zig/zig-source/lib/std/fs.zig:693
#4  0x00005555564bfd13 in Cache.Manifest.hit (self=0x7fffffff7aa0)
    at /home/timon/dev/zig/zig-source/src/Cache.zig:303
#5  0x00005555565b1c25 in glibc.buildSharedObjects (comp=0x55555e655f08)
    at /home/timon/dev/zig/zig-source/src/glibc.zig:716
#6  0x000055555657fa65 in Compilation.performAllTheWork (self=0x55555e655f08)
    at /home/timon/dev/zig/zig-source/src/Compilation.zig:1551
#7  0x00005555565796b9 in Compilation.update (self=0x55555e655f08)
    at /home/timon/dev/zig/zig-source/src/Compilation.zig:1290
#8  0x000055555651c877 in main.updateModule (gpa=0x55555e563cd0 <c_allocator_state>, 
    comp=0x55555e655f08, zir_out_path=..., hook=...)
    at /home/timon/dev/zig/zig-source/src/main.zig:1953
#9  0x000055555646a26e in main.buildOutputType (gpa=0x55555e563cd0 <c_allocator_state>, 
    arena=0x7fffffffdca8, all_args=..., arg_mode=...)
    at /home/timon/dev/zig/zig-source/src/main.zig:1796
#10 0x0000555556441a85 in main.mainArgs (gpa=0x55555e563cd0 <c_allocator_state>, 
    arena=0x7fffffffdca8, args=...) at /home/timon/dev/zig/zig-source/src/main.zig:167
#11 0x00005555564411ef in main (argc=4, argv=0x7fffffffdee8)
    at /home/timon/dev/zig/zig-source/src/stage1.zig:45

This can be reproduced as follows:
One terminal:

➜  zig-source git:(more-llvm-stage2) ✗ cat bug-stage2.zig 
const std = @import("std");

test "asdf" {
    while (true) {
        std.time.sleep(1000000000);
    }
}%                                                                                                                   
➜  zig-source git:(more-llvm-stage2) ✗ zig test bug-stage2.zig -lc
Test [1/1] test "asdf"... 

Then in the other terminal:

➜  zig-source git:(more-llvm-stage2) ✗ zig run mainstage2.c -lc

[andrewrk]

Related: #7596

[FireFox317]

Has been fixed in 7e5aaca

The glibc_so_files weren't deinitialized which caused a fd to stay open.