GenEx: Add tests for "0" and "1" expressions with literal commas.

Tests/GeneratorExpression/CMakeLists.txt

@@ -4,7 +4,9 @@ project(GeneratorExpression NONE)
 add_custom_target(check ALL
   COMMAND ${CMAKE_COMMAND}
     -Dtest_0=$<0:nothing>
+    -Dtest_0_with_comma=$<0:-Wl,--no-undefined>
     -Dtest_1=$<1:content>
+    -Dtest_1_with_comma=$<1:-Wl,--no-undefined>
     -Dconfig=$<CONFIGURATION>
     -Dtest_and_0=$<AND:0>
     -Dtest_and_0_0=$<AND:0,0>

Tests/GeneratorExpression/check.cmake

@@ -6,7 +6,9 @@ endmacro()
 
 message(STATUS "config=[${config}]")
 check(test_0 "")
+check(test_0_with_comma "")
 check(test_1 "content")
+check(test_1_with_comma "-Wl,--no-undefined")
 check(test_and_0 "0")
 check(test_and_0_0 "0")
 check(test_and_0_1 "0")