nail_11.21.bb: Fix build failure due to dumbness in a configure-like script.

nail_11.21.bb: Fix build failure due to dumbness in a configure-like script.

Presumably this build failure is due to a race condition, whereby the LIBS
file contains some garbage when it is autogenerated by the 'makeconfig' script.

mipsel-oe-linux-gcc -march=mips32 -L/mnt/oe/tmp/sysroots/mipsel-oe-linux/usr/lib -Wl,-rpath-link,/mnt/oe/tmp/sysroots/mipsel-oe-linux/usr/lib -Wl,-O1 aux.o base64.o cache.o cmd1.o cmd2.o cmd3.o cmdtab.o collect.o dotlock.o edit.o fio.o getname.o getopt.o head.o hmac.o imap.o imap_search.o junk.o lex.o list.o lzw.o macro.o maildir.o main.o md5.o mime.o names.o nss.o openssl.o pop3.o popen.o quit.o send.o sendout.o smtp.o ssl.o strings.o temp.o thread.o tty.o v7.local.o vars.o version.o `grep '^[^#]' LIBS`  -o nail
mipsel-oe-linux-gcc: o: No such file or directory
mipsel-oe-linux-gcc: make: No such file or directory
mipsel-oe-linux-gcc: grep: No such file or directory
mipsel-oe-linux-gcc: happy: No such file or directory
make: *** [nail] Error 1

Signed-off-by: Graham Gower <graham.gower@gmail.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>