It turns out some OSX system libraries (like CoreGraphics on 10.6) like
to call malloc_zone_* functions, but giving them pointers that weren't
allocated with the zone they are using.
Possibly, they do malloc_zone_malloc(malloc_default_zone()) before we
register the jemalloc zone, and malloc_zone_realloc(malloc_default_zone())
after. malloc_default_zone() returning a different value in both cases.
I tested a build from 10.7 run on 10.7 and 10.6, and a build from 10.6
run on 10.6. The AC_COMPILE_IFELSE limbo is to avoid running a program
during configure, which presumably makes it work when cross compiling
for iOS.
Add the --with-mangling configure option, which can be used to specify
name mangling on a per public symbol basis that takes precedence over
--with-jemalloc-prefix.
Expose the memalign() and valloc() overrides even if
--with-jemalloc-prefix is specified. This change does no real harm, and
simplifies the code.