Build zig-rpc-server for i686

cargo-zigbuild is replaced with a simple zig-cc wrapper.
cargo-zigbuild still tries to use i386-linux-musl triple,
while in zig 0.11 x86-linux-musl should be used [1].

This also gives us more control over compilation flags used
and prevents changes due to cargo-zigbuild upgrades,
as its version was not pinned.

[1] Merged PR "all: rename i386 to x86 "
    <https://github.com/ziglang/zig/pull/13101>

scripts/zig-cc

@@ -0,0 +1,32 @@
+#!/usr/bin/env python
+import subprocess
+import sys
+import os
+
+
+def flag_filter(flag: str) -> bool:
+    if flag == "-lc":
+        return False
+    if flag == "-Wl,-melf_i386":
+        return False
+    if "self-contained" in flag and "crt" in flag:
+        return False
+    return True
+
+
+def main():
+    args = [flag for flag in sys.argv[1:] if flag_filter(flag)]
+    zig_target = os.environ["ZIG_TARGET"]
+    zig_cpu = os.environ.get("ZIG_CPU")
+    if zig_cpu:
+        zig_cpu_args = ["-mcpu=" + zig_cpu]
+        args = [x for x in args if not x.startswith("-march")]
+    else:
+        zig_cpu_args = []
+
+    subprocess.run(
+        ["zig", "cc", "-target", zig_target, *zig_cpu_args, *args], check=True
+    )
+
+
+main()