[phb] Document USES=llvm

Which was introduced in:
https://cgit.FreeBSD.org/ports/commit/?id=2b3e37f30c249db5e9957c3ee41c25dea3191fc5

Reviewed by:	tcberner@
Differential Revision:	https://reviews.freebsd.org/D37737

1 files changed, 24 insertions, 0 deletions

diff --git a/documentation/content/en/books/porters-handbook/uses/_index.adoc b/documentation/content/en/books/porters-handbook/uses/_index.adoc
index eb30fe397d..ff44f7ae20 100644
--- a/documentation/content/en/books/porters-handbook/uses/_index.adoc
+++ b/documentation/content/en/books/porters-handbook/uses/_index.adoc
@@ -1075,6 +1075,30 @@ Specify `c7` to depend on CentOS 7 packages. The available packages are:
 * `ucl`
 * `xorglibs`
 
+[[uses-llvm]]
+== `llvm`
+
+Possible arguments: (none), `_XY_`, min=`_XY_`, max=`_XY_`, build, run, lib
+
+Adds a dependency on LLVM.
+By default this is a build dependency unless overridden by the `run` or `lib`
+options.
+The default version is the one set in `LLVM_DEFAULT`. A specific version can be
+specified as well. The minimum and maximum versions can be specified with the
+`min` and `max` parameters respectively.
+The ports framework export the following variables to the port:
+
+`LLVM_VERSION`::
+Version chosen from the arguments to llvm.mk
+`LLVM_PORT`::
+Chosen llvm port
+`LLVM_CONFIG`::
+llvm-config of the chosen port
+`LLVM_LIBLLVM`::
+libLLVM.so of the chosen port
+`LLVM_PREFIX`::
+Installation prefix of the chosen port
+
 [[uses-localbase]]
 == `localbase`