Help: Explain build/install-tree include dirs in more places (#14946)

Explain how to use $<BUILD_INTERFACE> and $<INSTALL_INTERFACE> directly
in the documentation of the target_include_directories command and
INTERFACE_INCLUDE_DIRECTORIES target property.  Otherwise readers need
to notice the link to the cmake-buildsystem(7) manual and find the
example in that to understand the need for these expressions.

Also fix the explanation in cmake-buildsystem(7) to not claim that
relative paths may be used inside a BUILD_INTERFACE expression.

1 files changed, 3 insertions, 3 deletions

diff --git a/Help/manual/cmake-buildsystem.7.rst b/Help/manual/cmake-buildsystem.7.rst
index 3e1f011..f3a5770 100644
--- a/Help/manual/cmake-buildsystem.7.rst
+++ b/Help/manual/cmake-buildsystem.7.rst
@@ -578,9 +578,9 @@ expands to the installation prefix when imported by a consuming project.
 Include directories usage requirements commonly differ between the build-tree
 and the install-tree.  The ``BUILD_INTERFACE`` and ``INSTALL_INTERFACE``
 generator expressions can be used to describe separate usage requirements
-based on the usage location.  Relative paths are allowed within these
-expressions, and are interpreted relative to the current source directory
-or the installation prefix, as appropriate:
+based on the usage location.  Relative paths are allowed within the
+``INSTALL_INTERFACE`` expression and are interpreted relative to the
+installation prefix.  For example:
 
 .. code-block:: cmake