tree cf6d2748b5016482d13dbc48b151ed71985ad0a1
parent 2ad14ef4ea57c19f6cb4ed365e99a30be81eefe7
author Brad King <brad.king@kitware.com> 1550068044 -0500
committer Brad King <brad.king@kitware.com> 1550070236 -0500

Update logic for sysroot in detected implicit include directories

Since commit 5990ecb741 (Compute implicit include directories from
compiler output, 2018-12-07, v3.14.0-rc1~108^2) the values of the
`CMAKE_<LANG>_IMPLICIT_INCLUDE_DIRECTORIES` variables are computed from
a real compiler invocation.  In this case the paths under the sysroot
should already have the sysroot prefix so we should no longer have to
add the sysroot prefix.  However, it is also possible for project code
to add its own paths to `CMAKE_<LANG>_IMPLICIT_INCLUDE_DIRECTORIES`
without the sysroot prefix and expect the historical addition of the
sysroot prefix to be preserved.

Try to account for both cases by conditionally adding the sysroot prefix
on implicit include directories that do not already have it.