[flang] Repair recent Power build bot breakage

Add AIX_WARNING expected warnings to a test that is now producing
new warnings.

Should fix https://lab.llvm.org/buildbot/#/builders/201/builds/2291.

Author: klausler

flang/test/Semantics/kinds04_q10.f90

@@ -11,11 +11,13 @@ subroutine s(var)
   real :: realvar3 = 4.0Q6
   !PORTABILITY: Explicit kind parameter together with non-'E' exponent letter is not standard
   real :: realvar4 = 4.0D6_8
+  !AIX_WARNING: underflow on REAL(10) to REAL(8) conversion
   !WARNING: Explicit kind parameter on real constant disagrees with exponent letter 'q'
   real :: realvar5 = 4.0Q6_10
   !PORTABILITY: Explicit kind parameter together with non-'E' exponent letter is not standard
   real :: realvar6 = 4.0Q6_16
   real :: realvar7 = 4.0E6_8
+  !AIX_WARNING: underflow on REAL(10) to REAL(8) conversion
   real :: realvar8 = 4.0E6_10
   real :: realvar9 = 4.0E6_16
   !ERROR: Unsupported REAL(KIND=32)
@@ -29,6 +31,7 @@ subroutine s(var)
   !PORTABILITY: Explicit kind parameter together with non-'E' exponent letter is not standard
   double precision :: doublevar5 = 4.0Q6_16
   double precision :: doublevar6 = 4.0E6_8
+  !AIX_WARNING: underflow on REAL(10) to REAL(8) conversion
   double precision :: doublevar7 = 4.0E6_10
   double precision :: doublevar8 = 4.0E6_16
   !ERROR: Unsupported REAL(KIND=32)