RISC-V: Enable RVC on ".option arch, +zca" etc.

Since the 'Zca' extension is the new base of the compressed instructions,
this commit enables RVC *also* when the 'Zca' extension is enabled
via ".option arch" directive.

gas/ChangeLog:

	* config/tc-riscv.c (s_riscv_option): Enable RVC also when the
	'Zca' extension is enabled after an ".option arch" directive.

Author: a4lg

gas/config/tc-riscv.c

@@ -4376,7 +4376,8 @@ s_riscv_option (int x ATTRIBUTE_UNUSED)
       riscv_reset_subsets_list_arch_str ();
 
       riscv_set_rvc (false);
-      if (riscv_subset_supports (&riscv_rps_as, "c"))
+      if (riscv_subset_supports (&riscv_rps_as, "c")
+	  || riscv_subset_supports (&riscv_rps_as, "zca"))
 	riscv_set_rvc (true);
 
       if (riscv_subset_supports (&riscv_rps_as, "ztso"))