nmon: not available on uclibc/musl

Fixes:
http://autobuild.buildroot.net/results/70c/70ce1aa234e321884469d04282f80750bcf9abc8/

nmon uses fstab.h which is only provided by glibc.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/nmon/Config.in

@@ -1,7 +1,11 @@
 config BR2_PACKAGE_NMON
 	bool "nmon"
+	depends on BR2_TOOLCHAIN_USES_GLIBC # fstab.h
 	select BR2_PACKAGE_NCURSES
 	help
 	  Nmon is short for Nigel's performance Monitor for Linux
 
 	  http://nmon.sourceforge.net/pmwiki.php
+
+comment "nmon needs a glibc toolchain"
+	depends on !BR2_TOOLCHAIN_USES_GLIBC