be: Let the backends themselves tell, whether they are experimental.

include/libfirm/be.h

@@ -97,6 +97,9 @@ typedef struct vararg_params {
  * propagated to the libFirm parameter set.
  */
 typedef struct backend_params {
+	/* Info whether this backend is unfinished. */
+	char const *experimental;
+
 	/** the backend uses big-endian byte ordering if set, else little endian */
 	unsigned byte_order_big_endian:1;
 	/** 1 if backend supports generation of position independent code (PIC) */

ir/be/TEMPLATE/bearch_TEMPLATE.c

@@ -139,6 +139,7 @@ static int TEMPLATE_is_mux_allowed(ir_node *sel, ir_node *mux_false,
 static const backend_params *TEMPLATE_get_backend_params(void)
 {
 	static backend_params p = {
+		.experimental                  = "The TEMPLATE backend is just a demo for writing backends",
 		.byte_order_big_endian         = false,
 		.pic_supported                 = false,
 		.unaligned_memaccess_supported = false,

ir/be/amd64/bearch_amd64.c

@@ -757,6 +757,7 @@ static const ir_settings_arch_dep_t amd64_arch_dep = {
 };
 
 static backend_params amd64_backend_params = {
+	.experimental                  = "the amd64 backend is highly experimental and unfinished (consider the ia32 backend)",
 	.byte_order_big_endian         = false,
 	.pic_supported                 = true,
 	.unaligned_memaccess_supported = true,

ir/be/arm/bearch_arm.c

@@ -260,6 +260,7 @@ static const ir_settings_arch_dep_t arm_arch_dep = {
 	.max_bits_for_mulh    = ARM_MACHINE_SIZE,
 };
 static backend_params arm_backend_params = {
+	.experimental                  = "the arm backend is highly experimental and unfinished",
 	.byte_order_big_endian         = false,
 	.pic_supported                 = false,
 	.unaligned_memaccess_supported = false,