Doc: Bump LLDB version requirement

Drop 179.x on OS X, as this barely works. Include 3.7 on Linux,
at least a build from SVN revision 232800 is knwon to be good.

Also change 'minimal supported version' to 'minimum supported
version'.

Change-Id: Ia491289500aa1d9680a3194cd50852aec65272d1
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>