build: adjust Makefile and test/run_examples.sh slightly to work with gentoo-like build environemnt

Makefile

@@ -79,7 +79,7 @@ vendor: $(VENDOR)
 version: $(GIT_REVISION)
 
 $(GIT_REVISION):
-	git rev-parse master > git_revision.txt
+	git rev-parse HEAD > git_revision.txt
 
 $(VENDOR):
 	rm -rf .cargo vendor vendor.tar.xz

tests/run_examples.sh

@@ -55,7 +55,11 @@ export EXAMPLES_DIR
 CPU_CORES=$(nproc --all)
 
 # Build debug binary
-cargo +$TOOLCHAIN build
+if [ $RUSTUP -eq 1 ]; then
+	cargo +$TOOLCHAIN build
+else
+	cargo build
+fi
 test_generic
 test_params