chibios: honor PLATFORMASM in chibios build (#11219)

tmk_core/chibios.mk

@@ -207,7 +207,7 @@ CHIBISRC = $(STARTUPSRC) \
        $(CHIBIOS)/os/various/syscalls.c
 
 # Ensure the ASM files are not subjected to LTO -- it'll strip out interrupt handlers otherwise.
-QUANTUM_LIB_SRC += $(STARTUPASM) $(PORTASM) $(OSALASM)
+QUANTUM_LIB_SRC += $(STARTUPASM) $(PORTASM) $(OSALASM) $(PLATFORMASM)
 
 CHIBISRC := $(patsubst $(TOP_DIR)/%,%,$(CHIBISRC))