Failure of ::realloc() should be handled correctly in loadlib_aix.cpp

[Split out from JDK-8217291]

In a few places of hotspot a possible failure of realloc isn't handled correctly: Either the return value isn't checked for NULL, of the original memory isn't freed, or both.

os/aix/loadlib_aix.cpp: buffer = (uint8_t*) ::realloc(buffer, buflen);
os/aix/loadlib_aix.cpp: char** l2 = (char**) ::realloc(_list, sizeof(char*) * cap2);