scripts: Clean up the logging in makefile.std and pnglibconf.mak

The console logs produced by these scripts should be easy to follow,
especially on CI bots.

Delete the unnecessary macros ECHO and SED.
Add a new macro MV_F (for "mv -f"), alongside RM_F (for "rm -f").
diff --git a/scripts/makefile.std b/scripts/makefile.std
index 25924e7..eec63b0 100644
--- a/scripts/makefile.std
+++ b/scripts/makefile.std
@@ -36,10 +36,9 @@
 LN_SF = ln -sf
 RANLIB = ranlib
 CP = cp
+MV_F = mv -f
 RM_F = rm -f
 AWK = awk
-SED = sed
-ECHO = echo
 
 DFNFLAGS = # DFNFLAGS contains -D options to use in the libpng build
 DFA_EXTRA = # extra files that can be used to control configuration
@@ -65,21 +64,21 @@
 # copy this if the following doesn't work.
 pnglibconf.h: pnglibconf.dfn
 	$(RM_F) $@ pnglibconf.c pnglibconf.out pnglibconf.tmp
-	$(ECHO) '#include "pnglibconf.dfn"' >pnglibconf.c
-	$(ECHO) "If '$(CC) -E' crashes try /lib/cpp (e.g. CPP='/lib/cpp')" >&2
+	echo '#include "pnglibconf.dfn"' >pnglibconf.c
+	@echo "## If '$(CC) -E' fails, try /lib/cpp (e.g. CPP='/lib/cpp')" >&2
 	$(CPP) $(DFNFLAGS) pnglibconf.c >pnglibconf.out
-	$(AWK) -f "scripts/dfn.awk" out="pnglibconf.tmp" pnglibconf.out 1>&2
-	mv pnglibconf.tmp $@
+	$(AWK) -f scripts/dfn.awk out=pnglibconf.tmp pnglibconf.out >&2
+	$(MV_F) pnglibconf.tmp $@
 
 pnglibconf.dfn: scripts/pnglibconf.dfa scripts/options.awk pngconf.h pngusr.dfa $(DFA_XTRA)
 	$(RM_F) $@ pnglibconf.pre pnglibconf.tmp
-	$(ECHO) "Calling $(AWK) from scripts/pnglibconf.mak" >&2
-	$(ECHO) "If 'awk' crashes try a better awk (e.g. AWK='nawk')" >&2
-	$(AWK) -f scripts/options.awk out="pnglibconf.pre"\
+	@echo "## Calling $(AWK) from scripts/pnglibconf.mak" >&2
+	@echo "## If 'awk' fails, try a better awk (e.g. AWK='nawk')" >&2
+	$(AWK) -f scripts/options.awk out=pnglibconf.pre\
 	    version=search pngconf.h scripts/pnglibconf.dfa\
-	    pngusr.dfa $(DFA_XTRA) 1>&2
-	$(AWK) -f scripts/options.awk out="pnglibconf.tmp" pnglibconf.pre 1>&2
-	mv pnglibconf.tmp $@
+	    pngusr.dfa $(DFA_XTRA) >&2
+	$(AWK) -f scripts/options.awk out=pnglibconf.tmp pnglibconf.pre >&2
+	$(MV_F) pnglibconf.tmp $@
 
 libpng.a: $(OBJS)
 	$(AR_RC) $@ $(OBJS)
diff --git a/scripts/pnglibconf.mak b/scripts/pnglibconf.mak
index c125ca2..34a240e 100755
--- a/scripts/pnglibconf.mak
+++ b/scripts/pnglibconf.mak
@@ -11,12 +11,12 @@
 AWK = mawk
 AWK = nawk
 AWK = one-true-awk
-AWK = awk  # Crashes on SunOS 5.10 - use 'nawk'
-CPP = $(CC) -E # On SUN OS 5.10 if this causes problems use /lib/cpp
+AWK = awk      # This fails on SunOS 5.10; use 'nawk'
+CPP = $(CC) -E # If this fails on SunOS 5.10, use '/lib/cpp'
 
-MOVE = mv
+MOVE = mv -f
 DELETE = rm -f
-ECHO = echo
+
 DFA_XTRA = # Put your configuration file here, see scripts/pnglibconf.dfa.  Eg:
 # DFA_XTRA = pngusr.dfa
 
@@ -25,27 +25,27 @@
 # as appropriate
 DFNFLAGS = $(DEFS) $(CPPFLAGS) $(CFLAGS)
 
-# srcdir is a defacto standard for the location of the source
+# srcdir is a de-facto standard for the location of the source
 srcdir = .
 
 # The standard pnglibconf.h exists as scripts/pnglibconf.h.prebuilt,
 # copy this if the following doesn't work.
 pnglibconf.h: pnglibconf.dfn
 	$(DELETE) $@ pnglibconf.c pnglibconf.out pnglibconf.tmp
-	$(ECHO) '#include "pnglibconf.dfn"' >pnglibconf.c
-	$(ECHO) "If '$(CC) -E' crashes try /lib/cpp (e.g. CPP='/lib/cpp')" >&2
+	echo '#include "pnglibconf.dfn"' >pnglibconf.c
+	@echo "## If '$(CC) -E' fails, try /lib/cpp (e.g. CPP='/lib/cpp')" >&2
 	$(CPP) $(DFNFLAGS) pnglibconf.c >pnglibconf.out
-	$(AWK) -f "$(srcdir)/scripts/dfn.awk" out="pnglibconf.tmp" pnglibconf.out 1>&2
+	$(AWK) -f $(srcdir)/scripts/dfn.awk out=pnglibconf.tmp pnglibconf.out >&2
 	$(MOVE) pnglibconf.tmp $@
 
 pnglibconf.dfn: $(srcdir)/scripts/pnglibconf.dfa $(srcdir)/scripts/options.awk $(srcdir)/pngconf.h $(srcdir)/pngusr.dfa $(DFA_XTRA)
 	$(DELETE) $@ pnglibconf.pre pnglibconf.tmp
-	$(ECHO) "Calling $(AWK) from scripts/pnglibconf.mak" >&2
-	$(ECHO) "If 'awk' crashes try a better awk (e.g. AWK='nawk')" >&2
-	$(AWK) -f $(srcdir)/scripts/options.awk out="pnglibconf.pre"\
+	@echo "## Calling $(AWK) from scripts/pnglibconf.mak" >&2
+	@echo "## If 'awk' fails, try a better awk (e.g. AWK='nawk')" >&2
+	$(AWK) -f $(srcdir)/scripts/options.awk out=pnglibconf.pre\
 	    version=search $(srcdir)/pngconf.h $(srcdir)/scripts/pnglibconf.dfa\
-	    $(srcdir)/pngusr.dfa $(DFA_XTRA) 1>&2
-	$(AWK) -f $(srcdir)/scripts/options.awk out="pnglibconf.tmp" pnglibconf.pre 1>&2
+	    $(srcdir)/pngusr.dfa $(DFA_XTRA) >&2
+	$(AWK) -f $(srcdir)/scripts/options.awk out=pnglibconf.tmp pnglibconf.pre >&2
 	$(MOVE) pnglibconf.tmp $@
 
 clean-pnglibconf: