fix(ci/edriver): link against zstd-static on Alpine instead of vendored-libelf

Alpine 3.20 libelf-static IS compiled WITH zstd support, so linking
system libelf.a introduces ZSTD_* symbol references.

Root cause of the new error:
- host == target on Alpine (both x86_64-unknown-linux-musl)
- Cargo resolver=2 only separates features when host != target; when
  they match, libbpf-sys features are unified between [dependencies]
  and [build-dependencies]
- static-libelf (from libbpf-rs/static) bleeds into the build-script
  compilation, causing the build.rs to emit cargo:rustc-link-lib=elf
  against the system libelf.a (which has ZSTD refs)

Fix: install zstd-static on Alpine and add '-l static=zstd' to RUSTFLAGS
so the linker can resolve ZSTD_* from /usr/lib/libzstd.a.
vendored-libelf is not used on Alpine to avoid the elfutils configure
argp/fts failure chain on musl.

Changes:
- matrix: add rustflags field per arch (x86_64 gets -lzstd, aarch64 doesn't)
- Alpine apk: add zstd-dev zstd-static
- Build/Test env: RUSTFLAGS uses matrix.rustflags
- Cache key bumped to v5

Author: chriskaliX

.github/workflows/ci-edriver.yaml

@@ -32,8 +32,13 @@ jobs:
             # zlib-static installs libz.a to /lib (not /usr/lib) on Alpine 3.20.
             lib_path: /lib:/usr/lib
             extra_cflags: ""
-            # Alpine libelf-static is musl-native, no zstd dep: no vendored-libelf.
+            # Alpine libelf-static is musl-native but IS compiled WITH zstd.
+            # We link against system zstd-static instead of using vendored-libelf
+            # (vendored-libelf fails on musl because elfutils configure requires
+            # glibc-only argp/fts).  The extra '-l static=zstd' tells rustc to
+            # include /usr/lib/libzstd.a when linking.
             cargo_extra_features: ""
+            rustflags: "-C target-feature=+crt-static -l static=zstd"
           - arch: aarch64
             runner: ubuntu-24.04-arm
             target: aarch64-unknown-linux-musl
@@ -48,7 +53,9 @@ jobs:
             # Ubuntu libelf is glibc-compiled: must vendored-compile elfutils.
             # elfutils configure needs argp+fts which exist on glibc (Ubuntu) but
             # not on musl (Alpine), hence this is Ubuntu-only.
+            # vendored-libelf is compiled --without-zstd, so no -lzstd needed.
             cargo_extra_features: ",vendored-libelf"
+            rustflags: "-C target-feature=+crt-static"
     steps:
       # ── Alpine (x86_64) ─────────────────────────────────────────────────
       # Install BEFORE actions/checkout so git/bash/curl are available for
@@ -62,6 +69,7 @@ jobs:
             clang llvm \
             elfutils-dev libelf-static \
             zlib-dev zlib-static \
+            zstd-dev zstd-static \
             protobuf-dev \
             pkgconf
 
@@ -98,8 +106,8 @@ jobs:
           path: |
             ~/.cargo/registry
             ~/.cargo/git
-          key: ${{ matrix.arch }}-cargo-edriver-v4-${{ hashFiles('plugins/edriver/Cargo.lock') }}
-          restore-keys: ${{ matrix.arch }}-cargo-edriver-v4-
+          key: ${{ matrix.arch }}-cargo-edriver-v5-${{ hashFiles('plugins/edriver/Cargo.lock') }}
+          restore-keys: ${{ matrix.arch }}-cargo-edriver-v5-
 
       - name: Verify toolchain
         run: |
@@ -122,7 +130,7 @@ jobs:
           CC_aarch64_unknown_linux_musl: ${{ matrix.cc }}
           CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_LINKER: ${{ matrix.cc }}
           CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_LINKER: ${{ matrix.cc }}
-          RUSTFLAGS: "-C target-feature=+crt-static"
+          RUSTFLAGS: ${{ matrix.rustflags }}
           # Activates vendored-libelf only on Ubuntu aarch64 (see matrix).
           CARGO_EXTRA_FEATURES: ${{ matrix.cargo_extra_features }}
 
@@ -138,5 +146,5 @@ jobs:
           CC_aarch64_unknown_linux_musl: ${{ matrix.cc }}
           CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_LINKER: ${{ matrix.cc }}
           CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_LINKER: ${{ matrix.cc }}
-          RUSTFLAGS: "-C target-feature=+crt-static"
+          RUSTFLAGS: ${{ matrix.rustflags }}
           CARGO_EXTRA_FEATURES: ${{ matrix.cargo_extra_features }}