Config.in files: add missing dependencies to toolchain option comments

When a package A depends on config option B and toolchain option C, then
the comment that is given when C is not fulfilled should also depend on B.
For example:

config BR2_PACKAGE_A
	depends on BR2_B
	depends on BR2_LARGEFILE
	depends on BR2_WCHAR

comment "A needs a toolchain w/ largefile, wchar"
	depends on !BR2_LARGEFILE || !BR2_WCHAR

This comment should actually be:

comment "A needs a toolchain w/ largefile, wchar"
	depends on BR2_B
	depends on !BR2_LARGEFILE || !BR2_WCHAR

or if possible (typically when B is a package config option declared in that
same Config.in file):

if BR2_B

comment "A needs a toolchain w/ largefile, wchar"
	depends on !BR2_LARGEFILE || !BR2_WCHAR

[other config options depending on B]

endif

Otherwise, the comment would be visible even though the other dependencies
are not met.

This patch adds such missing dependencies, and changes existing such
dependencies from
  depends on BR2_BASE_DEP && !BR2_TOOLCHAIN_USES_GLIBC
to
  depends on BR2_BASE_DEP
  depends on !BR2_TOOLCHAIN_USES_GLIBC
so that (positive) base dependencies are separate from the (negative)
toolchain dependencies. This strategy makes it easier to write such comments
(because one can simply copy the base dependency from the actual package
config option), but also avoids complex and long boolean expressions.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
 (untested)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>