android: aco: add aco_optimizer_postRA.cpp to Makefile.sources

Fixes the following building error:

external/mesa/src/amd/compiler/aco_interface.cpp:155: error: undefined reference to 'aco::optimize_postRA(aco::Program*)'

Fixes: 0e4747d3fb ("aco: Introduce a new, post-RA optimizer.")
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11177>

src/amd/Makefile.sources

@@ -111,6 +111,7 @@ ACO_FILES = \
 	compiler/aco_lower_to_cssa.cpp \
 	compiler/aco_lower_to_hw_instr.cpp \
 	compiler/aco_optimizer.cpp \
+	compiler/aco_optimizer_postRA.cpp \
 	compiler/aco_opt_value_numbering.cpp \
 	compiler/aco_print_asm.cpp \
 	compiler/aco_print_ir.cpp \