Relax requirements on asm for non-BIOS i386 platforms.

These platforms don't have a hard limit on size of resulting code16
code, so we don't care if assembly is bigger than necessarry.

asm-tests/i386-pc.S

@@ -0,0 +1,10 @@
+/* on x86 old clang doesn't support .code16
+   newer clang supports it but creates 6-byte jumps instead of 3-byte ones
+   which makes us go over boot sector size.  */
+
+	.code16
+	jmp far
+	.org 4
+	.space 300
+far:
+	.byte 0

asm-tests/i386.S

@@ -1,10 +1,4 @@
-/* on x86 old clang doesn't support .code16
-   newer clang supports it but creates 6-byte jumps instead of 3-byte ones
-   which makes us go over boot sector size.  */
+/* on x86 old clang doesn't support .code16  */
 
 	.code16
-	jmp far
-	.org 4
-	.space 300
-far:
-	.byte 0
+	movb %al, %bl

configure.ac

@@ -562,14 +562,17 @@ AC_COMPILE_IFELSE(
 
 AC_CACHE_CHECK([for options to compile assembly], [grub_cv_cc_target_asm_compile], [
 test_program=
-case "x$target_cpu" in
-     xmips | xmipsel)
+case "x$target_cpu-$platform" in
+     xmips-* | xmipsel-*)
         test_program=mips
 	;;
-     xi386 | xx86_64)
+     xi386-pc)
+       test_program=i386-pc
+	;;
+     xi386-* | xx86_64-*)
        test_program=i386
 	;;
-     xpowerpc | xsparc64 | xarm)
+     xpowerpc-* | xsparc64-* | xarm-*)
         test_program=$target_cpu
 	;;
 esac