Corrected the sky130 Makefile so that it does not throw an error
when generating the sky130B variant due to the missing Calibre-
derived OpenRCX rules files (which do not exist).  The error
causes the entire sky130B build to halt.

VERSION

diff --git a/VERSION b/VERSION
index 2ed9a2a..2587cf1 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.0.344
+1.0.345

sky130/Makefile.in

diff --git a/sky130/Makefile.in b/sky130/Makefile.in
index 94846cd..cfa5571 100644
--- a/sky130/Makefile.in
+++ b/sky130/Makefile.in
@@ -1051,12 +1051,19 @@
 	${CPP} ${SKY130$*_DEFS} openlane/rules.openrcx.sky130$*.max.spef_extractor \
 		${OPENLANE_STAGING_$*}/rules.openrcx.sky130$*.max.spef_extractor
 
-	${CPP} ${SKY130$*_DEFS} openlane/rules.openrcx.sky130$*.min.calibre \
-		${OPENLANE_STAGING_$*}/rules.openrcx.sky130$*.min.calibre
-	${CPP} ${SKY130$*_DEFS} openlane/rules.openrcx.sky130$*.nom.calibre \
-		${OPENLANE_STAGING_$*}/rules.openrcx.sky130$*.nom.calibre
-	${CPP} ${SKY130$*_DEFS} openlane/rules.openrcx.sky130$*.max.calibre \
-		${OPENLANE_STAGING_$*}/rules.openrcx.sky130$*.max.calibre
+	# Only install the calibre-derived rule files if they exist in the source
+	if test -f openlane/rules.openrcx.sky130$*.min.calibre ; then \
+		${CPP} ${SKY130$*_DEFS} openlane/rules.openrcx.sky130$*.min.calibre \
+			${OPENLANE_STAGING_$*}/rules.openrcx.sky130$*.min.calibre ;\
+	fi
+	if test -f openlane/rules.openrcx.sky130$*.nom.calibre ; then \
+		${CPP} ${SKY130$*_DEFS} openlane/rules.openrcx.sky130$*.nom.calibre \
+			${OPENLANE_STAGING_$*}/rules.openrcx.sky130$*.nom.calibre ;\
+	fi
+	if test -f openlane/rules.openrcx.sky130$*.max.calibre ; then \
+		${CPP} ${SKY130$*_DEFS} openlane/rules.openrcx.sky130$*.max.calibre \
+			${OPENLANE_STAGING_$*}/rules.openrcx.sky130$*.max.calibre ;\
+	fi
 
 	for file in ${OPENLANE_COMMON} ; do \
 	    ${CPP} -quiet ${SKY130$*_DEFS} openlane/sky130_fd_sc_hd/$$file \