I have some legacy F77 code, that test for NAN and infinite of real*8

I can link the code, using pgf77, if I use isnanf() and isinff() - but these two routines are not documented in the PGI manuals.

The modern routines would be ieee_is_nan() and ieee_is_finite(), but I can’t figure out how to include them in vanilla F77. In short, can I rewrite the F90 code:

```
program test
use, intrinsic::ieee_arithmetic
real *8 value
logical y
value=1.
y = ieee_is_nan(value)
print *, 'NAN(',v,')=', y
end program test
```

as something like:

```
program test
real *8 value
logical y
value=1.
y = ieee_is_nan(value)
print *, 'NAN(',v,')=', y
end
```

but this gives me:

% pgf77 -c testx.f

% pgf77 -o testx testx.o

testx.o: In function `test': /tmp/./testx.f:7: undefined reference to `

ieee_is_nan_’

pgf77 croakes on a USE statement, like

```
USE, INTRINSIC :: IEEE_ARITHMETIC
```

% pgf77 -c testx-ifort.f

PGFTN-S-0034-Syntax error at or near , (testx-ifort.f: 2)

0 inform, 0 warnings, 1 severes, 0 fatal for test

PGFTN/x86-64 Linux 13.9-0: compilation completed with severe errors

while ifort will compile and link

% ifort -c testx-ifort.f

% ifort -o testx-ifort testx-ifort.o

PS: I use pgf77 13.9