picocrt: Adapt x86 crt0 code for old clang assembler

Before clang-12, the built-in x86 assembler seems to treat prefixes as
separate instructions. This meant that it wouldn't allow them on the
same source line as the rest of the instruction. Split out the 'cs'
prefix used in the x86 crt0 code to a separate line so that old clang
versions can also assemble the code.

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

picocrt/machine/x86/crt0-32.S

@@ -45,7 +45,8 @@
 	.type	start, @function
 _start:
 	.code16
-	cs lgdtl gdt_desc - _start + 0x10
+	cs
+	lgdtl gdt_desc - _start + 0x10
 	mov $1, %eax
 	mov %eax, %cr0
 	ljmpl $0x10,$_start32

picocrt/machine/x86/crt0-64.S

@@ -45,7 +45,8 @@
 	.type	start, @function
 _start:
 	.code16
-	cs lgdtl	gdt_desc - _start + 0x10
+	cs
+	lgdtl	gdt_desc - _start + 0x10
 
 	# enable sse and pae
 	mov	$0x620, %eax