contrib: support disabling "LTO" in "nm-copr-build.sh"

The "nm-copr-build.sh" script is run by our copr to generate the SRPM of
NetworkManager (via `curl ... | bash`).

Building with LTO takes a long time, for testing it can be nice to disable
that. Add an environment variable for that. It can be used when manually
building an RPM in copr.

contrib/scripts/nm-copr-build.sh

@@ -2,7 +2,10 @@
 
 # environment variables:
 # - GIT_REF: the ref that should be build. Can be "main" or a git sha.
-# - DEBUG: set to 1 to build "--with debug".
+# - DEBUG: set to 1 to build "--with debug". Otherwise the default is a release
+#     build.
+# - LTO: set to 1/0 to build "--with/--without lto", otherwise the default depends
+#     on the distribution.
 # - NM_GIT_BUNDLE: set to a HTTP url where to fetch the nm-git-bundle-*.noarch.rpm
 #     from. Set to empty to skip it. By default, it fetches the bundle from copr.
 
@@ -14,6 +17,14 @@ else
     DEBUG="--without debug"
 fi
 
+if [ "$LTO" = 0 ]; then
+    LTO='--without -lto'
+elif [ "$LTO" = 1 ]; then
+    LTO='--with -lto'
+else
+    LTO=
+fi
+
 if [[ -z "$GIT_REF" ]]; then
     echo "\$GIT_REF is not set!"
     exit 1
@@ -59,7 +70,7 @@ GIT_SHA="$(git show-ref --verify --hash "$GIT_REF" 2>/dev/null ||
 
 git checkout -b tmp "$GIT_SHA"
 
-./contrib/fedora/rpm/build_clean.sh -g -S -w test $DEBUG -s copr
+./contrib/fedora/rpm/build_clean.sh -g -S -w test $DEBUG $LTO -s copr
 popd
 
 mv ./NetworkManager/contrib/fedora/rpm/latest/{SOURCES,SPECS}/* .