Revert "strip -Werror: all specific or none (#30284)" (#30878)

This reverts commit 330832c22c.

lib/spack/env/cc

@@ -401,8 +401,7 @@ input_command="$*"
 # command line and recombine them with Spack arguments later.  We
 # parse these out so that we can make sure that system paths come
 # last, that package arguments come first, and that Spack arguments
-# are injected properly.  Based on configuration, we also strip -Werror
-# arguments.
+# are injected properly.
 #
 # All other arguments, including -l arguments, are treated as
 # 'other_args' and left in their original order.  This ensures that
@@ -441,29 +440,6 @@ while [ $# -ne 0 ]; do
         continue
     fi
 
-    if [ -n "${SPACK_COMPILER_FLAGS_KEEP}" ] ; then
-        # NOTE: the eval is required to allow `|` alternatives inside the variable
-        eval "\
-        case '$1' in
-            $SPACK_COMPILER_FLAGS_KEEP)
-                append other_args_list "$1"
-                shift
-                continue
-                ;;
-        esac
-        "
-    fi
-    if [ -n "${SPACK_COMPILER_FLAGS_REMOVE}" ] ; then
-        eval "\
-        case '$1' in
-            $SPACK_COMPILER_FLAGS_REMOVE)
-                shift
-                continue
-                ;;
-        esac
-        "
-    fi
-
     case "$1" in
         -isystem*)
             arg="${1#-isystem}"