Zonestar P802M bed thermistor (#18289)

Co-authored-by: Scott Lahteine <github@thinkyhead.com>

platformio.ini

@@ -166,6 +166,16 @@ platform      = atmelavr
 extends       = env:melzi
 upload_speed  = 115200
 
+#
+# Melzi and clones (Zonestar Melzi2 with tuned flags)
+#
+[env:melzi_optimized]
+platform      = atmelavr
+extends       = env:melzi
+upload_speed  = 115200
+build_flags   = ${common.build_flags} -fno-tree-scev-cprop -fno-split-wide-types -Wl,--relax -mcall-prologues
+build_unflags = -g -ggdb
+
 #
 # AT90USB1286 boards using CDC bootloader
 # - BRAINWAVE