gfortran compiles
--------------------
      SUBROUTINE OPT1 (IB)
      IMPLICIT REAL*8 (A-H,O-Z)
      COMMON /INTNEW/ VL,EPS,BEGIN,STEP
      END

      SUBROUTINE OPT0(E0,H0,P0,NUMB,X,Y)
      IMPLICIT double precision (A-H,O-Z)
      COMMON /INTNEW/ V,EPS,BEGIN,STEP,PP,DOM,PIMEAN,AA,A0,BB,B0,PI0,G,G1,G2
      END
------------------
without any warning (as does ifort). However, you should either warn or give an error if two commons don't match.


NAGWare compiler fails with an ERROR:
------------------
Error: test5.f90: Inconsistent definitions of COMMON block INTNEW in program-units OPT1 and OPT0
------------------

g95 compiler (with only "-c" and not -Wall) compiles, but spits out the warning:
------------------
In file test5.f90:8
      COMMON /INTNEW/ V,EPS,BEGIN,STEP,PP,DOM,PIMEAN,AA,A0,BB,B0,PI0,G,G1,G2
                     1
In file test5.f90:3
      COMMON /INTNEW/ VL,EPS,BEGIN,STEP
                     2
Warning (121): COMMON block 'intnew' is 120 bytes at (1) and 32 bytes at (2)
------------------