docs/manual: rephrase paragraph about unsupported external toolchains

The ELDK now relies on Yocto, so it no longer has the funky
non-standard way of doing multilib. Also, we didn't mention that Yocto
toolchains/SDK are not suitable for usage with Buildroot. Therefore,
this commit rewords this part of the documentation to explain that
Yocto/OpenEmbedded SDKs cannot be used as external toolchains in
Buildroot, and why.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/configure.txt

@@ -179,23 +179,13 @@ Buildroot itself. In general, all toolchains that support the
 'sysroot' feature should work. If not, do not hesitate to contact the
 developers.
 
-We do not support toolchains from the
-http://www.denx.de/wiki/DULG/ELDK[ELDK] of Denx, for two reasons:
-
-* The ELDK does not contain a pure toolchain (i.e just the compiler,
-  binutils, the C and C++ libraries), but a toolchain that comes with
-  a very large set of pre-compiled libraries and programs. Therefore,
-  Buildroot cannot import the 'sysroot' of the toolchain, as it would
-  contain hundreds of megabytes of pre-compiled libraries that are
-  normally built by Buildroot.
-
-* The ELDK toolchains have a completely non-standard custom mechanism
-  to handle multiple library variants. Instead of using the standard
-  GCC 'multilib' mechanism, the ARM ELDK uses different symbolic links
-  to the compiler to differentiate between library variants (for ARM
-  soft-float and ARM VFP), and the PowerPC ELDK compiler uses a
-  +CROSS_COMPILE+ environment variable. This non-standard behaviour
-  makes it difficult to support ELDK in Buildroot.
+We do not support toolchains or SDK generated by OpenEmbedded or
+Yocto, because these toolchains are not pure toolchains (i.e just the
+compiler, binutils, the C and C++ libraries). Instead these toolchains
+come with a very large set of pre-compiled libraries and
+programs. Therefore, Buildroot cannot import the 'sysroot' of the
+toolchain, as it would contain hundreds of megabytes of pre-compiled
+libraries that are normally built by Buildroot.
 
 We also do not support using the distribution toolchain (i.e the
 gcc/binutils/C library installed by your distribution) as the