GHA: Fix / debug Linux build

Author: nicowilliams

.github/workflows/build-linux.yml

@@ -112,7 +112,7 @@ jobs:
             sudo debootstrap --arch=$(dpkg --print-architecture) focal sysroot-focal http://archive.ubuntu.com/ubuntu
           fi
           sudo chroot sysroot-focal apt-get update
-          sudo chroot sysroot-focal apt-get install -y build-essential git wget curl sudo unzip zip autoconf libfreetype6-dev libcups2-dev libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev libasound2-dev libffi-dev file binutils libfontconfig-dev
+          sudo chroot sysroot-focal apt-get install -y build-essential git wget curl sudo unzip zip autoconf libfreetype6-dev libcups2-dev libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev libasound2-dev libffi-dev file binutils libfontconfig-dev libc6-dev libpthread-stubs0-dev
           # If we really need gcc-10, we can get it from this PPA:
           sudo chroot sysroot-focal apt-get install -y software-properties-common
           sudo chroot sysroot-focal sudo add-apt-repository ppa:ubuntu-toolchain-r/test
@@ -121,6 +121,10 @@ jobs:
           echo $PWD
           ls -F
 
+      - name: 'Check pthread in sysroot'
+        run: |
+          find sysroot-focal -name 'libpthread.[sa]*' -ls
+
       - name: 'Get the BootJDK'
         id: bootjdk
         uses: ./.github/actions/get-bootjdk
@@ -181,6 +185,10 @@ jobs:
           echo PWD=$PWD &&
           exit 1)
 
+      - name: 'Check build config'
+        run: |
+          grep -E 'LDFLAGS|LIBS' build/*/spec.gmk build/*/bnuildjdk-spec.gmk || true
+
       - name: 'Build'
         id: build
         uses: ./.github/actions/do-build