CMake: Respect user-defined install path

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e97c64f..53399a1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -239,7 +239,6 @@
   endif()
 endif()
 
-set(CMAKE_INSTALL_PREFIX ${CMAKE_CURRENT_BINARY_DIR}/install)
 install(TARGETS ${SPIRV_BUILT_TARGETS}
   RUNTIME DESTINATION bin
   LIBRARY DESTINATION lib