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>

.github/workflows/deltachat-rpc-server.yml

@@ -15,7 +15,7 @@ jobs:
   # Build a version statically linked against musl libc
   # to avoid problems with glibc version incompatibility.
   build_linux:
-    name: Cross-compile deltachat-rpc-server for x86_64, aarch64 and armv7 Linux
+    name: Cross-compile deltachat-rpc-server for x86_64, i686, aarch64 and armv7 Linux
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v3
@@ -30,6 +30,13 @@ jobs:
           path: target/x86_64-unknown-linux-musl/release/deltachat-rpc-server
           if-no-files-found: error
 
+      - name: Upload i686 binary
+        uses: actions/upload-artifact@v3
+        with:
+          name: deltachat-rpc-server-i686
+          path: target/i686-unknown-linux-musl/release/deltachat-rpc-server
+          if-no-files-found: error
+
       - name: Upload aarch64 binary
         uses: actions/upload-artifact@v3
         with:
@@ -90,7 +97,7 @@ jobs:
       - name: Compose dist/ directory
         run: |
           mkdir dist
-          for x in x86_64 aarch64 armv7 win32.exe win64.exe; do
+          for x in x86_64 i686 aarch64 armv7 win32.exe win64.exe; do
             mv "deltachat-rpc-server-$x"/* "dist/deltachat-rpc-server-$x"
           done