[clang] [Clang][Docs][NFC] Correct documentation for the CPATH environment variable (PR #129113)

[Tom Honermann via cfe-commits]

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@@ -733,16 +733,17 @@ ENVIRONMENT
 
 .. envvar:: CPATH
 
-  If this environment variable is present, it is treated as a delimited list of
-  paths to be added to the default system include path list. The delimiter is
-  the platform dependent delimiter, as used in the PATH environment variable.
-
-  Empty components in the environment variable are ignored.
+  This environment variable specifies additional header file search paths which
+  behave as if they were specified with the :option:`-I\<directory\>` option at
+  the end of the driver command line. Paths are delimited by the platform
+  dependent delimiter as used in the ``PATH`` environment variable. Empty
+  components in the environment variable are ignored.
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tahonermann wrote:

For historical reference, that FIXME was introduced by https://github.com/llvm/llvm-project/commit/559865c89dcb9d4aff73828b9d89cc34a6c59229 by @d0k.

https://github.com/llvm/llvm-project/pull/129113