treewide: replace assert() with ASSERT() in special cases

treewide: replace assert() with ASSERT() in special cases

When the compiler/linker cannot verify that an assert() invocation is
free of side effects for us (e.g. because the assertion includes some
kind of function call), replace the use of assert() with ASSERT().

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>