Fix compiling on Solaris since Nate's libelf change

Fix compiling on Solaris since Nate's libelf change

SConstruct:
    export env after we've set CC/CXX
ext/libelf/SConscript:
    pull in the CC/CXX variables from env. Use gm4 if it exists
ext/libelf/elf_begin.c:
ext/libelf/libelf_allocate.c:
    include errno.h instead of sys/errno.h
ext/libelf/elf_common.h:
    use the more standard uintX_t
ext/libelf/elf_strptr.c:
ext/libelf/elf_update.c:
    include sysmacros.h on Solaris for roundup()

--HG--
extra : convert_revision : ea1aab834029399c445dfa4c9f78febf2c3d8f0c