Skip SectionMemoryManager.h in cpluspluscheck.

Commit 9044fc1d45 skipped SectionMemoryManager.h in headerscheck, and
by extension also cpluspluscheck, because it's C++ and would fail both
tests.  That worked in master and REL_17_STABLE due to 7b8e2ae2fd, but
older branches have a separate cpluspluscheck script.  We need to copy
the filtering rule into there too.

This problem was being reported by CI's CompilerWarnings task in the 15
and 16 branches, but was a victim of alert fatigue syndrome (unrelated
problems in the back-branches).

Fix 16, and back-patch to 13, as those are the live branches that have a
separate cpluspluscheck script.

src/tools/pginclude/cpluspluscheck

@@ -134,6 +134,9 @@ do
 	test "$f" = src/interfaces/ecpg/preproc/preproc.h && continue
 	test "$f" = src/test/isolation/specparse.h && continue
 
+	# SectionMemoryManager.h is C++
+	test "$f" = src/include/jit/SectionMemoryManager.h && continue
+
 	# ppport.h is not under our control, so we can't make it standalone.
 	test "$f" = src/pl/plperl/ppport.h && continue