manual: fix C++ support in libc case, fix indentation

The manual has this sentence for the dependency on a C library *and* a
toolchain feature:

    foo needs an (e)glibc toolchain, or foo needs an (e)glibc toolchain
    w/ C++ support

And then, just below, the comment text for C++ is just 'C++', not
'C++ support'.

Fix that, and add a bit of indentation too.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Samuel Martin <s.martin49@gmail.com>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>