Use default optimization of -Os for all ARMv6-M tools

arch/arm/src/armv6-m/Toolchain.defs

@@ -102,7 +102,6 @@ ifeq ($(CONFIG_ARMV6M_TOOLCHAIN),BUILDROOT)
   CROSSDEV ?= arm-nuttx-eabi-
   ARCROSSDEV ?= arm-nuttx-eabi-
   ARCHCPUFLAGS = -mcpu=cortex-m0 -mthumb -mfloat-abi=soft
-  MAXOPTIMIZATION = -Os
 endif
 
 # Code Red RedSuite under Linux
@@ -130,7 +129,6 @@ ifeq ($(CONFIG_ARMV6M_TOOLCHAIN),CODESOURCERYL)
   CROSSDEV ?= arm-none-eabi-
   ARCROSSDEV ?= arm-none-eabi-
   ARCHCPUFLAGS = -mcpu=cortex-m0 -mthumb -march=armv6-m -mfloat-abi=soft
-  MAXOPTIMIZATION = -Os
 endif
 
 # CodeSourcery under Windows
@@ -160,6 +158,10 @@ endif
 ifeq ($(CONFIG_ARMV6M_TOOLCHAIN),GNU_EABI)
   CROSSDEV ?= arm-none-eabi-
   ARCROSSDEV ?= arm-none-eabi-
-  MAXOPTIMIZATION = -Os
   ARCHCPUFLAGS = -mcpu=cortex-m0 -mthumb -march=armv6-m -mfloat-abi=soft
 endif  
+
+# Individual tools may limit the optimizatin level but, by default, the
+# optimization level will be set to to -Os
+
+MAXOPTIMIZATION ?= -Os