Rename value in top Makefile so it doesn't conflict.

`LIBRARIES` in the top Makefile would conflict with `LIBRARIES` in the
`scripts/make/git.mk`.

Signed-off-by: Tim 'mithro' Ansell <tansell@google.com>

Makefile

diff --git a/Makefile b/Makefile
index 1896b7e..ae7d4f7 100644
--- a/Makefile
+++ b/Makefile
@@ -79,9 +79,9 @@
 	@true
 
 
-LIBRARIES = $(sort $(notdir $(wildcard libraries/sky130_*_sc_*)))
+SC_LIBS = $(sort $(notdir $(wildcard libraries/sky130_*_sc_*)))
 
-$(LIBRARIES): | $(CONDA_ENV_PYTHON)
+$(SC_LIBS): | $(CONDA_ENV_PYTHON)
 	@$(IN_CONDA_ENV) for V in libraries/$@/*; do \
 		if [ -d "$$V/cells" ]; then \
 			python -m skywater_pdk.liberty $$V; \
@@ -99,7 +99,7 @@
 
 sky130_fd_sc_ms: sky130_fd_sc_ms-leakage
 
-timing: $(LIBRARIES) | $(CONDA_ENV_PYTHON)
+timing: $(SC_LIBS) | $(CONDA_ENV_PYTHON)
 	@true