drbd,dkms: try to find gcc used to build kernel

Some distributions use a separate (newer) compiler to build specific kernels.
This is a problem as the kernel config then often includes flags that the
default compiler does not understand.

Try to detect that in the DKMS build, sourcing the software collection that
contains a "good enough" compiler.

misc/dkms.conf

@@ -37,3 +37,27 @@ BUILT_MODULE_LOCATION[$IDX]="./src/drbd/build-current/drbd-kernel-compat/handsha
 DEST_MODULE_LOCATION[$IDX]="/kernel/net/handshake"
 fi
 fi
+
+# On some distros (OL8 for example), the default cc is not the one used to build the kernel.
+# In this case, the gcc is installed as a "Software Collection" which can be enabled.
+# So we try to find a compiler that matches the version used to build the original kernel.
+get_cc_version() {
+	if [ -n "$1" ]; then
+		scl run "$1" -- "/lib/modules/$kernelver/build/scripts/cc-version.sh" cc | cut -d' ' -f2
+	else
+		"/lib/modules/$kernelver/build/scripts/cc-version.sh" cc | cut -d' ' -f2
+	fi
+}
+
+if [ -e "/lib/modules/$kernelver/build/scripts/cc-version.sh" ]; then
+	KERNEL_GCC_VERSION="$(grep ^CONFIG_GCC_VERSION= "/lib/modules/$kernelver/build/.config" | cut -d= -f2)"
+
+	if [ "$KERNEL_GCC_VERSION" -gt "$(get_cc_version)" ] && command -v scl >/dev/null; then
+		for COLLECTION in $(scl list-collections); do
+			if [ "$KERNEL_GCC_VERSION" -le "$(get_cc_version "$COLLECTION")" ]; then
+				MAKE="scl run $COLLECTION -- $MAKE"
+				break
+			fi
+		done
+	fi
+fi