Make linux kernel string funcs available to tools

isspace() and strim() are not in the typical user-mode string.h, so
put them in a separate compilation unit so that they can be built into
tools that need them independent of the other common string functions.

This allows code shared by u-boot and the linux user-mode tools to link.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>

lib/Makefile

@@ -69,6 +69,7 @@ endif
 COBJS-y += crc32.o
 COBJS-y += ctype.o
 COBJS-y += div64.o
+COBJS-y += linux_string.o
 COBJS-y += string.o
 COBJS-y += time.o
 COBJS-$(CONFIG_BOOTP_PXE) += uuid.o