Add special value to RUNSQLSTM MARGINS keyword so command will detect width of source record and set margin to that width

Many of our SQL scripts are "vertically" long (number of lines) due to the rigid constraint of column 80 for MARGIN.

Although RUNSQLSTM MARGIN(constant-value) can be used, the requirement of the value being a constant makes transitioning to wider source files difficult. Any value other than "80" requires a hard-coded value in all places where the command is used.

To improve readability and lessen the number of lines in an SQL script, we create a "wider" source file:

CRTSRCPF FILE(SOMELIB/QSQLSTM) RCDLEN(112)

Various statements are added to source member SOMELIB/QSQLSTM SRCMBR(NEWTABLE); several statements extend past column 80.

This command is executed:
RUNSQLSTM SRCFILE(SOMELIB /QSQLSTM)
SRCMBR(NEWTABLE)
COMMIT(*NONE)
DFTRDBCOL(SOMELIB)

The command produces errors because keyword MARGINS defaults to 80.

This command results in a successful execution:
RUNSQLSTM SRCFILE(SOMELIB /QSQLSTM)
SRCMBR(NEWTABLE)
COMMIT(*NONE)
MARGINS(100)
DFTRDBCOL(SOMELIB)

If the RUNSQLSTM keyword MARGINS supported a special value -- *WIDTH for example, …

RUNSQLSTM SRCFILE(SOMELIB /QSQLSTM)
SRCMBR(NEWTABLE)
COMMIT(*NONE)
MARGINS(*WIDTH)
DFTRDBCOL(SOMELIB)

…the command would determine that SRCFILE(SOMELIB/QSQLSTM) has a width of 100 characters and use that value as if MARGINS(100) was specified.