Adds new tests for testing the parallel compilation engine.
They mainly test issues with regard to symbol promotion clash and
incorrect early assembler output.
* gcc.dg/parallel-early-constant.c: New test.
* gcc.dg/parallel-static-1.c: New test.
* gcc.dg/parallel-static-2.c: New test.
* gcc.dg/parallel-static-clash-1.c: New test.
* gcc.dg/parallel-static-clash-aux.c: New test.