Fix installation of SDCC files for deb/ubuntu

deb packages are built with a special libexecdir value, which makes
SDCC install some files in /usr/lib instead of /usr/z80-neogeo-ihx/lib
Since SDCC4.4 we no longer build support library or C library for the
z80, and on ubuntu this breaks later cleanup steps in install targets.
Update the install targets to fix installation on all supported
nightly packages (deb, rpm, brew, msys2).

Makefile

@@ -369,16 +369,18 @@ install-ngsdcc: $(BUILD)/ngsdcc
 	    rm -rf "$(DESTDIR)$(prefix)/z80-neogeo-ihx/include/asm/$$d"; \
 	    rm -rf "$(DESTDIR)$(prefix)/z80-neogeo-ihx/include/$$d"; \
 	done && \
-	find $(DESTDIR)$(prefix)/z80-neogeo-ihx/lib/ -mindepth 1 -type d -empty -delete && \
-	mkdir -p $(DESTDIR)$(prefix)/z80-neogeo-ihx/bin && \
-	(cd $(DESTDIR)$(prefix)/bin; \
+	if [ -d "$(DESTDIR)$(prefix)/z80-neogeo-ihx/lib" ]; then \
+	    find "$(DESTDIR)$(prefix)/z80-neogeo-ihx/lib" -mindepth 1 -type d -empty -delete; \
+	fi && \
+	mkdir -p "$(DESTDIR)$(prefix)/z80-neogeo-ihx/bin" && \
+	(cd "$(DESTDIR)$(prefix)/bin"; \
 	for f in `find . -name 'z80-neogeo-ihx-*'`; do \
 	    fbase=`echo $$f | cut -d- -f4`; \
-	    mv $$f $(DESTDIR)$(prefix)/z80-neogeo-ihx/bin/$$fbase; \
-	    echo "#!/bin/sh" > $(DESTDIR)$(prefix)/bin/$$f; \
-	    echo "PATH=$(prefix)/z80-neogeo-ihx/bin:\$$PATH" >> $(DESTDIR)$(prefix)/bin/$$f; \
-	    echo "$(prefix)/z80-neogeo-ihx/bin/$$fbase \$$@" >> $(DESTDIR)$(prefix)/bin/$$f; \
-	    chmod 755 $(DESTDIR)$(prefix)/bin/$$f; \
+	    mv $$f "$(DESTDIR)$(prefix)/z80-neogeo-ihx/bin/$$fbase"; \
+	    echo "#!/bin/sh" > "$(DESTDIR)$(prefix)/bin/$$f"; \
+	    echo "PATH=$(prefix)/z80-neogeo-ihx/bin:\$$PATH" >> "$(DESTDIR)$(prefix)/bin/$$f"; \
+	    echo "$(prefix)/z80-neogeo-ihx/bin/$$fbase \$$@" >> "$(DESTDIR)$(prefix)/bin/$$f"; \
+	    chmod 755 "$(DESTDIR)$(prefix)/bin/$$f"; \
 	done)