fix clean target for example makefiles if the compiler is not in PATH

Makefile

@@ -26,7 +26,7 @@ SHAREDIR	= $(DESTDIR)/$(PREFIX)/share/libopencm3/scripts
 INSTALL		= install
 
 SRCLIBDIR = $(shell pwd)/lib
-TARGETS = stm32/f1 stm32/f2 stm32/f4 lpc13xx lpc17xx lpc43xx lm3s 
+TARGETS = stm32/f1 stm32/f2 stm32/f4 lpc13xx lpc17xx lpc43xx lm3s
 
 # Be silent per default, but 'make V=1' will show all compiler calls.
 ifneq ($(V),1)

examples/lm3s/Makefile.include

@@ -24,14 +24,18 @@ CC		= $(PREFIX)-gcc
 LD		= $(PREFIX)-gcc
 OBJCOPY		= $(PREFIX)-objcopy
 OBJDUMP		= $(PREFIX)-objdump
+
+TOOLCHAIN_DIR ?= ../../../..
 ifeq ($(wildcard ../../../../lib/libopencm3_lm3s.a),)
+ifneq ($(strip $(shell which $(CC))),)
 TOOLCHAIN_DIR := $(shell dirname `which $(CC)`)/../$(PREFIX)
+endif
 else
 ifeq ($(V),1)
 $(info We seem to be building the example in the source directory. Using local library!)
 endif
-TOOLCHAIN_DIR := ../../../..
 endif
+
 CFLAGS		+= -O0 -g3 -Wall -Wextra -I$(TOOLCHAIN_DIR)/include -fno-common \
 		   -mcpu=cortex-m3 -mthumb -MD
 LDSCRIPT	?= $(BINARY).ld

examples/lpc13xx/Makefile.include

@@ -24,14 +24,18 @@ CC		= $(PREFIX)-gcc
 LD		= $(PREFIX)-gcc
 OBJCOPY		= $(PREFIX)-objcopy
 OBJDUMP		= $(PREFIX)-objdump
+
+TOOLCHAIN_DIR ?= ../../../..
 ifeq ($(wildcard ../../../../lib/libopencm3_lpc13xx.a),)
+ifneq ($(strip $(shell which $(CC))),)
 TOOLCHAIN_DIR := $(shell dirname `which $(CC)`)/../$(PREFIX)
+endif
 else
 ifeq ($(V),1)
 $(info We seem to be building the example in the source directory. Using local library!)
 endif
-TOOLCHAIN_DIR := ../../../..
 endif
+
 CFLAGS		+= -Os -g -Wall -Wextra -I$(TOOLCHAIN_DIR)/include -fno-common \
 		   -mcpu=cortex-m3 -mthumb -MD
 LDSCRIPT	?= $(BINARY).ld

examples/lpc17xx/Makefile.include

@@ -24,14 +24,18 @@ CC		= $(PREFIX)-gcc
 LD		= $(PREFIX)-gcc
 OBJCOPY		= $(PREFIX)-objcopy
 OBJDUMP		= $(PREFIX)-objdump
+
+TOOLCHAIN_DIR ?= ../../../..
 ifeq ($(wildcard ../../../../lib/libopencm3_lpc17xx.a),)
+ifneq ($(strip $(shell which $(CC))),)
 TOOLCHAIN_DIR := $(shell dirname `which $(CC)`)/../$(PREFIX)
+endif
 else
 ifeq ($(V),1)
 $(info We seem to be building the example in the source directory. Using local library!)
 endif
-TOOLCHAIN_DIR := ../../../..
 endif
+
 CFLAGS		+= -O0 -g -Wall -Wextra -I$(TOOLCHAIN_DIR)/include -fno-common \
 		   -mcpu=cortex-m3 -mthumb -MD
 LDSCRIPT	?= $(BINARY).ld

examples/lpc43xx/Makefile.include

@@ -27,14 +27,18 @@ LD		= $(PREFIX)-gcc
 OBJCOPY		= $(PREFIX)-objcopy
 OBJDUMP		= $(PREFIX)-objdump
 GDB		= $(PREFIX)-gdb
+
+TOOLCHAIN_DIR ?= ../../../..
 ifeq ($(wildcard ../../../../lib/libopencm3_lpc43xx.a),)
+ifneq ($(strip $(shell which $(CC))),)
 TOOLCHAIN_DIR := $(shell dirname `which $(CC)`)/../$(PREFIX)
+endif
 else
 ifeq ($(V),1)
 $(info We seem to be building the example in the source directory. Using local library!)
 endif
-TOOLCHAIN_DIR := ../../../..
 endif
+
 CFLAGS		+= -O2 -g -Wall -Wextra -I$(TOOLCHAIN_DIR)/include -fno-common \
 		   -mcpu=cortex-m4 -mthumb -MD \
 		   -mfloat-abi=hard -mfpu=fpv4-sp-d16

examples/stm32/f1/Makefile.include

@@ -25,14 +25,18 @@ LD		= $(PREFIX)-gcc
 OBJCOPY		= $(PREFIX)-objcopy
 OBJDUMP		= $(PREFIX)-objdump
 GDB		= $(PREFIX)-gdb
+
+TOOLCHAIN_DIR ?= ../../../../..
 ifeq ($(wildcard ../../../../../lib/libopencm3_stm32f1.a),)
+ifneq ($(strip $(shell which $(CC))),)
 TOOLCHAIN_DIR := $(shell dirname `which $(CC)`)/../$(PREFIX)
+endif
 else
 ifeq ($(V),1)
-$(info We seem to be building the example in the source directory. Using local library!) 
+$(info We seem to be building the example in the source directory. Using local library!)
 endif
-TOOLCHAIN_DIR := ../../../../..
 endif
+
 ARCH_FLAGS      = -mthumb -mcpu=cortex-m3 -msoft-float
 CFLAGS		+= -Os -g -Wall -Wextra -I$(TOOLCHAIN_DIR)/include \
 		   -fno-common $(ARCH_FLAGS) -MD -DSTM32F1

examples/stm32/f2/Makefile.include

@@ -26,14 +26,18 @@ LD		= $(PREFIX)-gcc
 OBJCOPY		= $(PREFIX)-objcopy
 OBJDUMP		= $(PREFIX)-objdump
 GDB		= $(PREFIX)-gdb
+
+TOOLCHAIN_DIR ?= ../../../../..
 ifeq ($(wildcard ../../../../../lib/libopencm3_stm32f2.a),)
+ifneq ($(strip $(shell which $(CC))),)
 TOOLCHAIN_DIR := $(shell dirname `which $(CC)`)/../$(PREFIX)
+endif
 else
 ifeq ($(V),1)
 $(info We seem to be building the example in the source directory. Using local library!)
 endif
-TOOLCHAIN_DIR := ../../../../..
 endif
+
 CFLAGS		+= -Os -g -Wall -Wextra -I$(TOOLCHAIN_DIR)/include \
 		   -fno-common -mcpu=cortex-m3 -mthumb -msoft-float -MD -DSTM32F2
 LDSCRIPT	?= $(BINARY).ld

examples/stm32/f4/Makefile.include

@@ -27,14 +27,18 @@ OBJCOPY		= $(PREFIX)-objcopy
 OBJDUMP		= $(PREFIX)-objdump
 GDB		= $(PREFIX)-gdb
 FLASH		= $(shell which st-flash)
+
+TOOLCHAIN_DIR ?= ../../../../..
 ifeq ($(wildcard ../../../../../lib/libopencm3_stm32f4.a),)
+ifneq ($(strip $(shell which $(CC))),)
 TOOLCHAIN_DIR := $(shell dirname `which $(CC)`)/../$(PREFIX)
+endif
 else
 ifeq ($(V),1)
 $(info We seem to be building the example in the source directory. Using local library!)
 endif
-TOOLCHAIN_DIR := ../../../../..
 endif
+
 CFLAGS		+= -Os -g -Wall -Wextra -I$(TOOLCHAIN_DIR)/include \
 		   -fno-common -mcpu=cortex-m4 -mthumb \
 		   -mfloat-abi=hard -mfpu=fpv4-sp-d16 -MD -DSTM32F4