fortran: Fix o'...' boz to integer/real conversions [PR96859]

fortran: Fix o'...' boz to integer/real conversions [PR96859]

The standard says that excess digits from boz are truncated.
For hexadecimal or binary, the routines copy just the number of digits
that will be needed, but for octal we copy number of digits that
contain one extra bit (for 8-bit, 32-bit or 128-bit, i.e. kind 1, 4 and 16)
or two extra bits (for 16-bit or 64-bit, i.e. kind 2 and 8).
The clearing of the first bit is done correctly by changing the first digit
if it is 4-7 to one smaller by 4 (i.e. modulo 4).
The clearing of the first two bits is done by changing 4 or 6 to 0
and 5 or 7 to 1, which is incorrect, because we really want to change the
first digit to 0 if it was even, or to 1 if it was odd, so digits
2 and 3 are mishandled by keeping them as is, rather than changing 2 to 0
and 3 to 1.

2020-09-02  Jakub Jelinek  <jakub@redhat.com>

	PR fortran/96859
	* check.c (gfc_boz2real, gfc_boz2int): When clearing first two bits,
	change also '2' to '0' and '3' to '1' rather than just handling '4'
	through '7'.

	* gfortran.dg/pr96859.f90: New test.