[arch][arm] avoid using -mgeneral-regs-only for arm32

For older compilers (gcc 7.5.0 in particular) avoid using
-mgeneral-regs-only to override the floating point switches, since it
doesn't seem to understand that switch.

Instead more properly add the floating point switches for a module or
source file compiled with float. More compatible with all compilers.

arch/arm/rules.mk

@@ -244,12 +244,14 @@ MODULE_SRCS += \
 	$(LOCAL_DIR)/arm/cache.c \
 	$(LOCAL_DIR)/arm/debug.c \
 	$(LOCAL_DIR)/arm/ops.S \
-	$(LOCAL_DIR)/arm/exceptions.S \
 	$(LOCAL_DIR)/arm/faults.c \
-	$(LOCAL_DIR)/arm/fpu.c \
 	$(LOCAL_DIR)/arm/mmu.c \
 	$(LOCAL_DIR)/arm/thread.c
 
+MODULE_FLOAT_SRCS += \
+	$(LOCAL_DIR)/arm/exceptions.S \
+	$(LOCAL_DIR)/arm/fpu.c \
+
 MODULE_ARM_OVERRIDE_SRCS := \
 	$(LOCAL_DIR)/arm/arch.c
 
@@ -333,8 +335,8 @@ TOOLCHAIN_PREFIX := $(ARCH_$(ARCH)_TOOLCHAIN_PREFIX)
 $(info TOOLCHAIN_PREFIX = $(TOOLCHAIN_PREFIX))
 
 ARCH_COMPILEFLAGS += $(ARCH_$(ARCH)_COMPILEFLAGS)
-ARCH_COMPILEFLAGS_NOFLOAT := -mgeneral-regs-only
-ARCH_COMPILEFLAGS_FLOAT :=
+ARCH_COMPILEFLAGS_NOFLOAT :=
+ARCH_COMPILEFLAGS_FLOAT := $(ARCH_$(ARCH)_COMPILEFLAGS_FLOAT)
 
 GLOBAL_COMPILEFLAGS += $(THUMBINTERWORK)
 

arch/arm/toolchain.mk

@@ -75,33 +75,31 @@ ARCH_arm_COMPILEFLAGS += -mcpu=cortex-m4
 endif
 ifeq ($(ARM_CPU),cortex-m7-fpu-sp-d16)
 # use cortex-m4 for now until better general toolchain support
-ARCH_arm_COMPILEFLAGS += -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp
+ARCH_arm_COMPILEFLAGS += -mcpu=cortex-m4
+ARCH_arm_COMPILEFLAGS_FLOAT += -mfpu=fpv4-sp-d16 -mfloat-abi=softfp
 endif
 ifeq ($(ARM_CPU),cortex-m4f)
-ARCH_arm_COMPILEFLAGS += -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp
+ARCH_arm_COMPILEFLAGS += -mcpu=cortex-m4
+ARCH_arm_COMPILEFLAGS_FLOAT += -mfpu=fpv4-sp-d16 -mfloat-abi=softfp
 endif
 ifeq ($(ARM_CPU),cortex-a7)
 ARCH_arm_COMPILEFLAGS += -mcpu=$(ARM_CPU)
-ARCH_arm_COMPILEFLAGS += -mfpu=vfpv3 -mfloat-abi=softfp
+ARCH_arm_COMPILEFLAGS_FLOAT += -mfpu=vfpv3 -mfloat-abi=softfp
 endif
 ifeq ($(ARM_CPU),cortex-a8)
 ARCH_arm_COMPILEFLAGS += -mcpu=$(ARM_CPU)
-ARCH_arm_COMPILEFLAGS += -mfpu=neon -mfloat-abi=softfp
+ARCH_arm_COMPILEFLAGS_FLOAT += -mfpu=neon -mfloat-abi=softfp
 endif
 ifeq ($(ARM_CPU),cortex-a9)
 ARCH_arm_COMPILEFLAGS += -mcpu=$(ARM_CPU)
 endif
 ifeq ($(ARM_CPU),cortex-a9-neon)
 ARCH_arm_COMPILEFLAGS += -mcpu=cortex-a9
-# XXX cannot enable neon right now because compiler generates
-# neon code for 64bit integer ops
-ARCH_arm_COMPILEFLAGS += -mfpu=vfpv3 -mfloat-abi=softfp
+ARCH_arm_COMPILEFLAGS_FLOAT += -mfpu=neon -mfloat-abi=softfp
 endif
 ifeq ($(ARM_CPU),cortex-a15)
 ARCH_arm_COMPILEFLAGS += -mcpu=$(ARM_CPU)
-ifneq ($(ARM_WITHOUT_VFP_NEON),true)
-ARCH_arm_COMPILEFLAGS += -mfpu=vfpv3 -mfloat-abi=softfp
-endif
+ARCH_arm_COMPILEFLAGS_FLOAT += -mfpu=neon -mfloat-abi=softfp
 endif
 ifeq ($(ARM_CPU),arm1136j-s)
 ARCH_arm_COMPILEFLAGS += -mcpu=$(ARM_CPU)
@@ -113,7 +111,7 @@ ifeq ($(ARM_CPU),cortex-r4f)
 ARCH_arm_COMPILEFLAGS += -march=armv7-r
 ARCH_arm_COMPILEFLAGS += -mcpu=$(ARM_CPU)
 ARCH_arm_COMPILEFLAGS += -mbig-endian
-ARCH_arm_COMPILEFLAGS += -mfpu=vfpv3-d16 -mfloat-abi=hard
+ARCH_arm_COMPILEFLAGS_FLOAT += -mfpu=vfpv3-d16 -mfloat-abi=hard
 GLOBAL_MODULE_LDFLAGS += -EB
 endif
 ifeq ($(ARM_CPU),armemu)