Introduce libzigc for libc function implementations in Zig.

This lays the groundwork for #2879. This library will be built and linked when a
static libc is going to be linked into the compilation. Currently, that means
musl, wasi-libc, and MinGW-w64. As a demonstration, this commit removes the musl
C code for a few string functions and implements them in libzigc. This means
that those libzigc functions are now load-bearing for musl and wasi-libc.

Note that if a function has an implementation in compiler-rt already, libzigc
should not implement it. Instead, as we recently did for memcpy/memmove, we
should delete the libc copy and rely on the compiler-rt implementation.

I repurposed the existing "universal libc" code to do this. That code hadn't
seen development beyond basic string functions in years, and was only usable-ish
on freestanding. I think that if we want to seriously pursue the idea of Zig
providing a freestanding libc, we should do so only after defining clear goals
(and non-goals) for it. See also #22240 for a similar case.

1 files changed, 6 insertions, 5 deletions

diff --git a/src/link/Coff.zig b/src/link/Coff.zig
index da27c5c076..4b20ba99dd 100644
--- a/src/link/Coff.zig
+++ b/src/link/Coff.zig
@@ -2147,6 +2147,12 @@ fn linkWithLLD(coff: *Coff, arena: Allocator, tid: Zcu.PerThread.Id, prog_node:
             },
         }
 
+        if (comp.config.link_libc and link_in_crt) {
+            if (comp.zigc_static_lib) |zigc| {
+                try argv.append(try zigc.full_object_path.toString(arena));
+            }
+        }
+
         // libc++ dep
         if (comp.config.link_libcpp) {
             try argv.append(try comp.libcxxabi_static_lib.?.full_object_path.toString(arena));
@@ -2172,11 +2178,6 @@ fn linkWithLLD(coff: *Coff, arena: Allocator, tid: Zcu.PerThread.Id, prog_node:
         }
 
         if (is_exe_or_dyn_lib and !comp.skip_linker_dependencies) {
-            if (!comp.config.link_libc) {
-                if (comp.libc_static_lib) |lib| {
-                    try argv.append(try lib.full_object_path.toString(arena));
-                }
-            }
             // MSVC compiler_rt is missing some stuff, so we build it unconditionally but
             // and rely on weak linkage to allow MSVC compiler_rt functions to override ours.
             if (comp.compiler_rt_obj) |obj| try argv.append(try obj.full_object_path.toString(arena));