chips/samd21: Make linker script compatible with Picolibc 1.8

Picolibc 1.8 initialization code requires TLS alignment values
computed by the linker script.

Signed-off-by: Keith Packard <keithp@keithp.com>

chips/samd21/snek-samd21.ld

@@ -125,6 +125,9 @@ SECTIONS {
 	} >ram AT>ram :tls :ram
 	PROVIDE(__tbss_size = SIZEOF(.tbss));
 	PROVIDE(__tls_size = __tls_end - __tls_base);
+	PROVIDE( __tls_align = MAX(ALIGNOF(.tdata), ALIGNOF(.tbss)) );
+	PROVIDE( __arm32_tls_tcb_offset = MAX(8, __tls_align) );
+	PROVIDE( __arm64_tls_tcb_offset = MAX(16, __tls_align) );
 
 	/*
 	 * The linker special cases .tbss segments which are