set PKG_CONFIG_ALLOW_CROSS and PKG_CONFIG_PATH for cross builds

Author: GyulyVGC

.github/workflows/package.yml

@@ -124,6 +124,16 @@ jobs:
           # and can't co-install with the host's amd64 copy; let the target arch's version win
           sudo apt-get install -y -o Dpkg::Options::=--force-overwrite \
             libpcap-dev:${{ matrix.arch }} libasound2-dev:${{ matrix.arch }}
+          # point pkg-config at the target arch's .pc files so -sys build scripts cross-compile
+          case "${{ matrix.arch }}" in
+            i386)  triple=i386-linux-gnu ;;
+            armhf) triple=arm-linux-gnueabihf ;;
+            arm64) triple=aarch64-linux-gnu ;;
+          esac
+          {
+            echo "PKG_CONFIG_ALLOW_CROSS=1"
+            echo "PKG_CONFIG_PATH=/usr/lib/$triple/pkgconfig"
+          } >> "$GITHUB_ENV"
 
       # build against glibc 2.28 so releases keep running on older distros (fixes #1256)
       - name: Build binary (Linux)