Avoid spurious libgcc-s1 Debian package dependency

Do not add a strict dependency on gcc, which in a GitHub container isn't
necessarily the same version as in a pristine Ubuntu system.

Fixes: #5875

Author: tautschnig

.github/workflows/pull-request-checks.yaml

@@ -407,6 +407,7 @@ jobs:
         run: |
           cd build
           ninja package
+          ls
           deb_package_name="$(ls *.deb)"
           echo "::set-output name=deb_package::./build/$deb_package_name"
           echo "::set-output name=deb_package_name::ubuntu-18.04-$deb_package_name"

cmake/packaging.cmake

@@ -25,7 +25,8 @@ set(CPACK_PACKAGE_RESOURCE_FILE_README "${CMAKE_CURRENT_SOURCE_DIR}/README.md")
 set(CPACK_DEBIAN_PACKAGE_SHLIBDEPS YES)
 
 # In addition, we depend on gcc for preprocessing
-set(CPACK_DEBIAN_PACKAGE_DEPENDS gcc)
+set(CPACK_DEBIAN_PACKAGE_RECOMMENDS gcc)
+set(CPACK_DEBIAN_PACKAGE_DEBUG YES)
 
 # For windows we need to set up product and update GUID
 # See: https://docs.microsoft.com/en-us/windows/win32/msi/productcode