use-correct-dwarf-default: Update test

* The default version is now 5. If clang version is older than 18 then
  fall back to version 4.
* Added optional env var to overwrite required dwarf version.
* Updated fmf metadata to use dwarf4 in distros that don't support v5
* Fedora 38 is EOL, removed dead code.

tests/use-correct-dwarf-default/main.fmf

@@ -25,3 +25,7 @@ adjust+:
       - llvm-toolset-15.0-clang
       - llvm-toolset-15.0-llvm
     when: "collection == llvm-toolset-15.0"
+
+  - environment+:
+      DWARF_VERSION: 4
+    when: distro < rhel-10 or distro < centos-stream-10

tests/use-correct-dwarf-default/runtest.sh

@@ -1,23 +1,16 @@
 #!/bin/sh -eux
 
-# Determine correct DWARF version to use. If Clang is newer or equal to version
-# 18, we want to use DWARF5 except for Fedora 38 where we still want DWARF4.
-
-required_dwarf_version=4
+# Determine correct DWARF version to use. Defaults to version 5, but older
+# distros might need to use version 4, which can be configured using the
+# DWARF_VERSION env var
+required_dwarf_version=${DWARF_VERSION:-5}
 
 # Get clang version
 CLANG_PKG=$(rpm -qf --queryformat '%{name}' $(readlink -f $(type -p clang)))
 clang_version=$(rpm -q --queryformat "%{version}" $CLANG_PKG | grep -ioP "^[0-9]+")
-if  [ $clang_version -ge 18 ]; then
-    >&2 echo "clang is greater or equal version 18";
-    required_dwarf_version=5
-fi
-
-if [ -e /etc/fedora-release ]; then
-    fedora_version=$(grep -ioP "Fedora release \K[0-9]+" /etc/fedora-release)
-    if [ $fedora_version -le 38 ]; then
-        required_dwarf_version=4
-    fi
+if  [ $clang_version -lt 18 ]; then
+    >&2 echo "clang is older than version 18";
+    required_dwarf_version=4
 fi
 
 echo "int main(){ return 0; }" | clang -g -v -x c - 2> build.log