external toolchain: Only prefix path if specified

Only prefix the external toolchain calls with its absolute path if
BR2_TOOLCHAIN_EXTERNAL_PATH is set, otherwise just assume it will
be available in the path.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/Makefile.in

@@ -115,7 +115,11 @@ TOOLCHAIN_EXTERNAL_LOCATION=$(TOOLCHAIN_EXTERNAL_DIR)
 else
 TOOLCHAIN_EXTERNAL_LOCATION=$(call qstrip,$(BR2_TOOLCHAIN_EXTERNAL_PATH))
 endif
+ifneq ($(TOOLCHAIN_EXTERNAL_LOCATION),)
 TARGET_CROSS=$(TOOLCHAIN_EXTERNAL_LOCATION)/bin/$(TOOLCHAIN_EXTERNAL_PREFIX)-
+else
+TARGET_CROSS=$(TOOLCHAIN_EXTERNAL_PREFIX)-
+endif
 endif
 
 # Quotes are needed for spaces et al in path components.