feat: enhance build_musl.sh with robust retry logic for installation

- Added a global wget configuration to handle transient HTTP errors and improve resilience during tarball downloads.
- Implemented an outer retry loop around the `make install` command to manage potential failures, allowing up to four attempts with exponential backoff.
- This enhancement ensures a more reliable build process when using musl-cross-make, particularly in environments with variable mirror quality.

Author: scc-tw

common/build/deplib/build_musl.sh

@@ -1,6 +1,23 @@
 #!/bin/bash
 
 set -euo pipefail
+
+# musl-cross-make pulls binutils/gmp/mpc/mpfr/gcc tarballs through
+# ftpmirror.gnu.org, which is a redirector that routes to mirrors of
+# wildly varying quality. When a redirect lands on a sad mirror the
+# response is HTTP 502 and the wget invocation inside their Makefile
+# gives up after one try, killing the entire build. We make wget retry
+# 5xx responses globally so musl-cross-make's untouched Makefile gets
+# the resilience for free.
+mkdir -p /etc
+cat > /etc/wgetrc <<'WGETRC'
+tries = 10
+waitretry = 10
+timeout = 60
+retry_connrefused = on
+retry_on_http_error = 408,429,500,502,503,504
+WGETRC
+
 git clone --depth 1 https://github.com/25077667/musl-cross-make.git
 
 cp ./config.mak musl-cross-make/config.mak
@@ -11,7 +28,24 @@ if [ -z "${OUTPUT_DIR}" ]; then
 fi
 
 cd musl-cross-make
-make -j "$(nproc)" install
+# Outer retry around the whole `make install`. musl-cross-make uses
+# `wget -c` for resumption, so a retried run picks up partial tarballs
+# rather than redownloading. Belt-and-braces with the wgetrc above:
+# wgetrc handles per-request transient errors; this loop covers the
+# case where the same tarball fails its full retry budget on a
+# completely-down mirror window.
+attempt=0
+max_attempts=4
+until make -j "$(nproc)" install; do
+    attempt=$((attempt + 1))
+    if [ "$attempt" -ge "$max_attempts" ]; then
+        echo "build_musl.sh: make install failed after $attempt attempts" >&2
+        exit 1
+    fi
+    backoff=$((attempt * 30))
+    echo "build_musl.sh: make install failed (attempt $attempt/$max_attempts), retrying in ${backoff}s..." >&2
+    sleep "$backoff"
+done
 
 OUTPUT_PATH="${OUTPUT_DIR}"