getpagesize(), as well as its POSIX.2001 replacement
sysconf(_SC_PAGESIZE), is defined in <unistd.h>. On Linux and OS X,
including <sys/mman.h> is sufficient to get a definition for
getpagesize(). However, this is not true for the Android NDK. This CL
brings back the HAVE_UNISTD_H definition and its associated header
check.
This also adds a HAVE_FUNC_SYSCONF definition, which checks for the
presence of sysconf(). The definition can be used later to replace
getpagesize() with sysconf().
Unused macros: HAVE_DLFCN_H, HAVE_INTTYPES_H, HAVE_MEMORY_H,
HAVE_STDLIB_H, HAVE_STRINGS_H, HAVE_STRING_H, HAVE_SYS_BYTESWAP_H,
HAVE_SYS_STAT_H, HAVE_SYS_TYPES_H, HAVE_UNISTD_H.
Used but never set macros: HAVE_LIBLZF, HAVE_LIBQUICKLZ. These only gate
conditional includes. The code that takes advantage of them was removed.
Unused types: ssize_t.
The testing code uses HAVE_FUNC_MMAP, which was not wired in the CMake
build, causing a whole test to be skipped.
