[make] default WITH_LINKER_GC to false at the place it is used

Also switch the test logic to the TOBOOL macro.

arch/m68k/rules.mk

@@ -16,10 +16,8 @@ ifndef TOOLCHAIN_PREFIX
 TOOLCHAIN_PREFIX := m68k-elf-
 endif
 
-WITH_LINKER_GC ?= 0
-
 # select the cpu based on flags the platform/target passes in
-M68K_CPU ?= 68040
+M68K_CPU ?= 68040 # default to 040
 
 ifeq ($(M68K_CPU),68000)
 ARCH_COMPILEFLAGS := -mcpu=68000

arch/microblaze/rules.mk

@@ -24,8 +24,6 @@ ifndef TOOLCHAIN_PREFIX
 TOOLCHAIN_PREFIX := microblaze-elf-
 endif
 
-WITH_LINKER_GC ?= 0
-
 LITTLE_ENDIAN ?= 0
 
 ifneq ($(LITTLE_ENDIAN),0)

arch/mips/rules.mk

@@ -26,7 +26,6 @@ ifndef TOOLCHAIN_PREFIX
 TOOLCHAIN_PREFIX := mips-elf-
 endif
 
-WITH_LINKER_GC ?= 0
 LITTLE_ENDIAN ?= 0
 
 ifneq ($(LITTLE_ENDIAN),0)

make/build.mk

@@ -1,7 +1,9 @@
 # use linker garbage collection, if requested
-ifeq ($(WITH_LINKER_GC),1)
+WITH_LINKER_GC ?= false
+ifeq (true,$(call TOBOOL,$(WITH_LINKER_GC)))
 GLOBAL_COMPILEFLAGS += -ffunction-sections -fdata-sections
 GLOBAL_LDFLAGS += --gc-sections
+GLOBAL_DEFINES += LINKER_GC=1
 endif
 
 ifneq (,$(EXTRA_BUILDRULES))