rtl-ssa: Define INCLUDE_ARRAY

rtl-ssa: Define INCLUDE_ARRAY

g:72fbd3b2b2a497dbbe6599239bd61c5624203ed0 added a use of std::array
without explicitly forcing <array> to be included.  That didn't cause
problems in my local builds but understandably did for some people.

gcc/
	* doc/rtl.texi: Document the need to define INCLUDE_ARRAY before
	including rtl-ssa.h.
	* rtl-ssa.h: Likewise (in comment).
	* config/aarch64/aarch64-cc-fusion.cc: Add INCLUDE_ARRAY.
	* config/aarch64/aarch64-early-ra.cc: Likewise.
	* config/riscv/riscv-avlprop.cc: Likewise.
	* config/riscv/riscv-vsetvl.cc: Likewise.
	* fwprop.cc: Likewise.
	* late-combine.cc: Likewise.
	* pair-fusion.cc: Likewise.
	* rtl-ssa/accesses.cc: Likewise.
	* rtl-ssa/blocks.cc: Likewise.
	* rtl-ssa/changes.cc: Likewise.
	* rtl-ssa/functions.cc: Likewise.
	* rtl-ssa/insns.cc: Likewise.
	* rtl-ssa/movement.cc: Likewise.