Compile.zig: Fix static->dynamic library linkage

[JacobCrabill]

I think this should solve this issue: #19341

Thanks to @andrewrk for pointing me to the relevant portion of Compile.zig to find the cause (and for pointing out the resultant issue in the archive file).

Reproducing the issue

• Define a dynamic library, dynamic-lib, from dynamic.c exporting a function void foo()
• Define a static library, static-lib, from static.c exporting a function void bar() { foo(); }
• Do static_lib.linkLibrary(dynamic_lib);
• Define an executable that links static-lib and dynamic-lib
• The error message will appear from lld while processing file libstatic-lib.a

Explanation of the issue

The error occurs because the archive file libstatic-lib.a contains symbols from the dynamic library libdynamic-lib.so, which is not valid for an archive file (static library).

$ nm -A  .zig-cache/o/.../libstatic-lib.a
.zig-cache/o/.../libstatic-lib.a:.zig-cache/o/.../libshared-lib.so:00000000000012e0 T bar       <-- BAD
.zig-cache/o/.../libstatic-lib.a:.zig-cache/o/.../libshared-lib.so:0000000000002300 d _DYNAMIC  <-- BAD
.zig-cache/o/.../libstatic-lib.a:.zig-cache/o/.../static.o:                 U bar
.zig-cache/o/.../libstatic-lib.a:.zig-cache/o/.../static.o:0000000000000000 T foo
.zig-cache/o/.../libstatic-lib.a:.zig-cache/o/.../static.o:0000000000000000 r .LCPI0_0
.zig-cache/o/.../libstatic-lib.a:.zig-cache/o/.../static.o:0000000000000004 r .LCPI0_1

The problematic command is the build-lib command to build the archive, which includes the .so file as a source:

zig build-lib /path/to//static-shared-error/src/static.c .zig-cache/o/.../libshared-lib.so -rpath .zig-cache/o/... -ODebug -I /path/to//static-shared-error/src -I .zig-cache/o/... -Mroot --cache-dir .zig-cache --global-cache-dir /home/jacob/.cache/zig --name static-lib -static --zig-lib-dir /path/to/zig/0.15.1/lib/

Note that both the static.c and libshared-lib.so files are given as position arguments to the build-lib command.

After these changes:

zig build-lib /path/to/static-shared-error/src/static.c -ODebug -I /path/to/static-shared-error/src -I .zig-cache/o/... -Mroot --cache-dir .zig-cache --global-cache-dir /home/jacob/.cache/zig --name static-lib -static --zig-lib-dir /path/to/zig/0.15.1/lib/

The .so file isn't listed, the error message does not appear, and the executable is still properly linked.

System Libraries

The above shows the issue with user-defined libraries, but this occurs with system libraries as well (as pointed out in the linked issue). To view a reproduction, clone https://github.com/zig-gamedev/zglfw/ (referenced from this comment) and build with Zig 0.14.1.

Testing

I only have a Linux machine to test on; not sure if there would be any linker-related differences on Mac or Windows that might cause issues.