GnuCOBOL defines compilation variables when various conditions are true.
If the condition associated with a variable is false, the variable is not defined.

DEBUG       The -d debug flag is specified.
EXECUTABLE  Module being compiled contains the main program.
GCCOMP      The size of a COMP item is determined according to the GnuCOBOL scheme,
            where for a picture of length:
             1 - 2,  item = 1 byte
             3 - 4,  item = 2 bytes
             5 - 9,  item = 4 bytes
            10 - 18, item = 8 bytes.

GNUCOBOL    GnuCOBOL is compiling the source unit.
HOSTSIGNS   A signed packed decimal item's value may be considered NUMERIC if
            sign = X"F".
IBMCOMP     The size of a COMP item is determined according to the IBM scheme,
            where for a PICTURE of length :
             1 - 4,  item = 2 bytes
             5 - 9,  item = 4 bytes
            10 - 18, item = 8 bytes.

MODULE      The element being compiled does not contain the main program.
NOHOSTSIGNS A signed packed decimal item's value may NOT be considered
            NUMERIC if sign = X"F".
NOIBMCOMP   The size of a COMP item is NOT determined according to the IBM scheme.
NOSTICKY-LINKAGE
            Sticky linkage (linkage section items remaining allocated between
            invocations) is NOT active.
NOTRUNC     Numeric data items are truncated according to their internal
            representation.
P64         Pointers are greater than 32 bits.
STICKY-LINKAGE
            Sticky linkage (linkage section items remaining allocated between
            invocations) is active.
TRUNC       Numeric data items are truncated according to their PICTURE clauses.

These, while still supported may well be removed in the future and should not be
used. See GCCOMP and GNUCOBOL instead:

OCCOMP      The size of a COMP item is determined according to the GnuCOBOL scheme,
            where for a PICTURE of length :
             1 - 2,  item = 1 byte
             3 - 4,  item = 2 bytes
             5 - 9,  item = 4 bytes
            10 - 18, item = 8 bytes.

OPENCOBOL   GnuCOBOL is compiling the source unit.
