[NFC][UR] Clarify the wording of urProgramLink[Exp] (#19237)

These functions allow the adapter to optionally provide an output
program for the build log. The way this was worded in the spec is a bit
unclear, so now it's been reworded.

There should be no change in behaviour in regards to the original
intent.

Author: RossBrunton

unified-runtime/include/ur_api.h

@@ -95,7 +95,7 @@ analogue:
 details:
     - "The application may call this function from simultaneous threads."
     - "Following a successful call to this entry point the program returned in `phProgram` will contain a binary of the $X_PROGRAM_BINARY_TYPE_EXECUTABLE type for each device in `phDevices`."
-    - "If a non-success code is returned and `phProgram` is not `nullptr`, it will contain an unspecified program or `nullptr`. Implementations may use the build log of this program (accessible via $xProgramGetBuildInfo) to provide an error log for the linking failure."
+    - "If a non-success code is returned, adapters may store a program in `phProgram`. This program should only be used with `$xProgramGetBuildInfo` to get the build log for the failure. Adapters which do not do not support producing build logs must set this value to `nullptr`."
 params:
     - type: $x_context_handle_t
       name: hContext

unified-runtime/scripts/core/exp-multi-device-compile.yml

@@ -227,7 +227,7 @@ analogue:
 details:
     - "The application may call this function from simultaneous threads."
     - "Following a successful call to this entry point the program returned in `phProgram` will contain a binary of the $X_PROGRAM_BINARY_TYPE_EXECUTABLE type for each device in `hContext`."
-    - "If a non-success code is returned and `phProgram` is not `nullptr`, it will contain an unspecified program or `nullptr`. Implementations may use the build log of this program (accessible via $xProgramGetBuildInfo) to provide an error log for the linking failure."
+    - "If a non-success code is returned, adapters may store a program in `phProgram`. This program should only be used with `$xProgramGetBuildInfo` to get the build log for the failure. Adapters which do not do not support producing build logs must set this value to `nullptr`."
 params:
     - type: $x_context_handle_t
       name: hContext