When the CMake option "LESS_DEBUG_INFO" was remamed to
"SWIFTSHADER_LESS_DEBUG_INFO", we forgot to rename it in the Kokoro
scripts.

Change-Id: I706be61af3a959cf99294491437fb9a968a6164b
Bug: none
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/44268Reviewed-by: Ben Clayton <bclayton@google.com>
Presubmit-Ready: Antonio Maiorano <amaiorano@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>