x86-64: Fix long long bug
x86-64: Fix long long bug

With the last improvements to lexpand it's now harmful
to use on native 64bit platforms when not necessary.  For gv_dup
it's not necessary there.  It can still be used with really
transforming a 64bit value into two 32bit ones.

andreiw/tinycc,mingodad/tinycc,run4flat/tinycc,andreiw/tinycc,mirror/tinycc,avih/tinycc,andreiw/tinycc,mirror/tinycc,avih/tinycc,mirror/tinycc,code4game/tinycc,run4flat/tinycc,avih/tinycc,run4flat/tinycc,avih/tinycc,code4game/tinycc,run4flat/tinycc,mingodad/tinycc,code4game/tinycc,mirror/tinycc,run4flat/tinycc,mingodad/tinycc,mingodad/tinycc