Add and test gcd().

libraries/base/common/hdllib.cfg

@@ -191,6 +191,7 @@ test_bench_files =
     tb/vhdl/tb_common_transpose_symbol.vhd
     tb/vhdl/tb_common_zip.vhd
     tb/vhdl/tb_common_variable_delay.vhd
+    tb/vhdl/tb_common_gcd.vhd
     tb/vhdl/tb_requantize.vhd
     tb/vhdl/tb_resize.vhd
     tb/vhdl/tb_round.vhd
@@ -224,6 +225,7 @@ regression_test_vhdl =
     tb/vhdl/tb_common_shiftreg.vhd
     tb/vhdl/tb_common_transpose_symbol.vhd
     tb/vhdl/tb_common_variable_delay.vhd
+    tb/vhdl/tb_common_gcd.vhd
     tb/vhdl/tb_tb_resize.vhd
     tb/vhdl/tb_tb_round.vhd
     tb/vhdl/tb_requantize.vhd