CI: output build errors as GitHub annotations

Author: renaudallard

.github/workflows/build.yml

@@ -66,7 +66,13 @@ jobs:
         uses: actions/checkout@v6
 
       - name: Build
-        run: make
+        run: |
+          make 2>&1 | tee /tmp/build.log || {
+            while IFS= read -r line; do
+              echo "::error::$line"
+            done < /tmp/build.log
+            exit 1
+          }
 
       - name: Verify binary
         run: ./thinproxy -V
@@ -126,7 +132,13 @@ jobs:
         uses: actions/checkout@v6
 
       - name: Build
-        run: make
+        run: |
+          make 2>&1 | tee /tmp/build.log || {
+            while IFS= read -r line; do
+              echo "::error::$line"
+            done < /tmp/build.log
+            exit 1
+          }
 
       - name: Verify binary
         run: ./thinproxy -V