Use a smaller AOM_MAX_ALLOCABLE_MEMORY for msan. (#1647)
Use a smaller AOM_MAX_ALLOCABLE_MEMORY for msan. (#1647)

The test cases for bug 9497 and bug 9499 cause out-of-memory errors
under msan but not under asan and ubsan. (This seems to imply msan has a
higher memory overhead.) Use a smaller AOM_MAX_ALLOCABLE_MEMORY value of
512 MB (as opposed to 1 GB) for msan.

BUG=oss-fuzz:9497
BUG=oss-fuzz:9499
skia-dev/oss-fuzz,robertswiecki/oss-fuzz,googlefonts/oss-fuzz,FeliciaLim/oss-fuzz,skia-dev/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,google/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,skia-dev/oss-fuzz,robertswiecki/oss-fuzz,googlefonts/oss-fuzz,googlefonts/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,robertswiecki/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,skia-dev/oss-fuzz,skia-dev/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,FeliciaLim/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,robertswiecki/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,googlefonts/oss-fuzz,robertswiecki/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,google/oss-fuzz,skia-dev/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,robertswiecki/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,google/oss-fuzz,google/oss-fuzz,googlefonts/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,googlefonts/oss-fuzz,skia-dev/oss-fuzz