Respect *FLAGS and toolchain variables in Makefiles where missing.
--- a/Makefile
+++ b/Makefile
@@ -12,3 +12,3 @@
 CFLAGS+=-I. -Wall -W -Wno-implicit-fallthrough -Wno-format-truncation \
--Wno-stringop-overflow -O3 -fsigned-char
+-Wno-stringop-overflow -fsigned-char
 # Enable -Wstringop-overflow[=type] when it is no longer a broken, partial
@@ -19,3 +19,2 @@
 # ld: warning: option -s is obsolete and being ignored
-LDFLAGS+=-s
 endif
--- a/backup/libcd64/Makefile
+++ b/backup/libcd64/Makefile
@@ -1,2 +1 @@
-CC=gcc
 
@@ -7,3 +6,2 @@
 else
-CFLAGS+=-O6 -funroll-loops -fexpensive-optimizations
 endif
@@ -181,4 +179,4 @@
 else
-	ld -r $^ $(LIBS) -o $*.o
-	ar crs $@ $*.o
+	$(LD) -r $^ $(LIBS) -o $*.o
+	$(AR) crs $@ $*.o
 endif
--- a/libdiscmage/Makefile.in
+++ b/libdiscmage/Makefile.in
@@ -33,3 +33,2 @@
 # /usr/bin/libtool: -static not specified, -s invalid
-LDFLAGS+=-s
 endif