Workaround 'condition is redundant or null deref is possible' cppcheck FP

Workaround 'condition is redundant or null deref is possible' cppcheck FP

* cord/cordprnt.c (MACRO_BLKSTMT_BEGIN, MACRO_BLKSTMT_END): New macro.
* cord/tests/de.c (MACRO_BLKSTMT_BEGIN, MACRO_BLKSTMT_END): Likewise.
* include/private/gc_priv.h (MACRO_BLKSTMT_BEGIN, MACRO_BLKSTMT_END):
Likewise.
* cord/cordprnt.c (OUT_OF_MEMORY): Use MACRO_BLKSTMT_BEGIN/END instead
of "do {" and "} while (0)".
* cord/tests/de.c (OUT_OF_MEMORY): Likewise.
* include/private/gc_priv.h (ABORT_ARG1, ABORT_ARG2, ABORT_ARG3):
Likewise.