build: Update scripts/makefile.*

Apply the following updates:
 * Tidy up the compiler flag definitions.
 * Update the Darwin, Linux and MSYS makefiles to match the compiler
   flags used in scripts/makefile.clang and scripts/makefile.gcc.
 * Add the `pngtest-static` target in the Darwin makefile, following
   on the Linux makefile.
 * Rewrite some of the implicit make rules to match one another more
   consistently.
 * Make corrections in the copyright years to match git log.

scripts/makefile.beos

@@ -1,6 +1,6 @@
 # makefile for libpng on BeOS x86 ELF with gcc
 # modified from makefile.linux by Sander Stoks
-# Copyright (C) 2020-2024 Cosmin Truta
+# Copyright (C) 2020-2025 Cosmin Truta
 # Copyright (C) 2002, 2006, 2008, 2010-2014 Glenn Randers-Pehrson
 # Copyright (C) 1999 Greg Roelofs
 # Copyright (C) 1996, 1997 Andreas Dilger
@@ -33,14 +33,10 @@ ALIGN=
 # For i386:
 # ALIGN=-malign-loops=2 -malign-functions=2
 
-WARNMORE=-Wwrite-strings -Wpointer-arith -Wshadow \
-	-Wmissing-declarations -Wtraditional -Wcast-align \
-	-Wstrict-prototypes -Wmissing-prototypes # -Wconversion
-
 # On BeOS, -O1 is actually better than -O3.  This is a known bug but it's
 # still here in R4.5
 CPPFLAGS=-I$(ZLIBINC) # -DPNG_DEBUG=5
-CFLAGS=-O1 -funroll-loops $(ALIGN) -Wall -Wextra -Wundef # $(WARNMORE) -g
+CFLAGS=-O1 -funroll-loops $(ALIGN) # -g
 ARFLAGS=rc
 # LDFLAGS=-L. -Wl,-rpath,. -L$(ZLIBLIB) -Wl,-rpath,$(ZLIBLIB) -lpng -lz
 LDFLAGS=-L. -Wl,-soname=$(LIBSOMAJ) -L$(ZLIBLIB) -lz # -g
@@ -58,7 +54,7 @@ OBJSDLL = $(OBJS)
 .SUFFIXES:      .c .o
 
 .c.o:
-	$(CC) -c $(CPPFLAGS) $(CFLAGS) -o $@ $<
+	$(CC) -c $(CPPFLAGS) $(CFLAGS) -o $@ $*.c
 
 all: libpng.a $(LIBSO) pngtest