cmake: Remove "conditions" from endif

See https://cmake.org/cmake/help/latest/command/endif.html and
https://cmake.org/cmake/help/latest/command/if.html.

If the else/endif condition does not match the if condition verbatim,
an error is produced on some versions of cmake. This change removes
these "legacy conditions."

SPIRV/CMakeLists.txt

@@ -101,12 +101,12 @@ if(ENABLE_OPT)
         $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/External>)
 else()
     target_link_libraries(SPIRV PRIVATE MachineIndependent)
-endif(ENABLE_OPT)
+endif()
 
 if(WIN32)
     source_group("Source" FILES ${SOURCES} ${HEADERS})
     source_group("Source" FILES ${SPVREMAP_SOURCES} ${SPVREMAP_HEADERS})
-endif(WIN32)
+endif()
 
 if(ENABLE_GLSLANG_INSTALL)
     if(BUILD_SHARED_LIBS)
@@ -135,4 +135,4 @@ if(ENABLE_GLSLANG_INSTALL)
     install(EXPORT SPIRVTargets DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake)
 
     install(FILES ${HEADERS} ${SPVREMAP_HEADERS} DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/glslang/SPIRV/)
-endif(ENABLE_GLSLANG_INSTALL)
+endif()