[Flang] Error during macro expension of mathematical expression at compile time.

[JDPailleux]

Hello,
I encountered a problem in the Ramses project that used the macro as follows:

program test
#if NVAR > 2
print *, "YES"
#else
print *, "NO"
#endif
end program
When I compile with gfortran with -cpp -DNVAR=2+1+0+0, it doesn't raise an error and the mathematical expression was expand and evaluated correctly.
However, with Flang, this was not the case and the macro was expanded as a string, which is not valid normally.

Issue also referenced in PR #166785

[llvmbot]

@llvm/issue-subscribers-bug

Author: Jean-Didier PAILLEUX (JDPailleux)

Hello, I encountered a problem in the [Ramses](https://github.com/ramses-organisation/ramses/) project that used the macro as follows:

program test
#if NVAR > 2
print *, "YES"
#else
print *, "NO"
#endif
end program
When I compile with gfortran with -cpp -DNVAR=2+1+0+0, it doesn't raise an error and the mathematical expression was expand and evaluated correctly.
However, with Flang, this was not the case and the macro was expanded as a string, which is not valid normally.

Issue also referenced in PR #166785

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Jean-Didier PAILLEUX (JDPailleux)

Hello, I encountered a problem in the [Ramses](https://github.com/ramses-organisation/ramses/) project that used the macro as follows:

program test
#if NVAR > 2
print *, "YES"
#else
print *, "NO"
#endif
end program
When I compile with gfortran with -cpp -DNVAR=2+1+0+0, it doesn't raise an error and the mathematical expression was expand and evaluated correctly.
However, with Flang, this was not the case and the macro was expanded as a string, which is not valid normally.

Issue also referenced in PR #166785