cortexm-m-generic: Make the linker script LTO-safe by making sure the vector table is always retained

lib/cortex-m-generic.ld

@@ -43,7 +43,7 @@ ENTRY(reset_handler)
 SECTIONS
 {
 	.text : {
-		*(.vectors)	/* Vector table */
+		KEEP(*(.vectors)) /* Vector table */
 		*(.text*)	/* Program code */
 		. = ALIGN(4);
 		*(.rodata*)	/* Read-only data */
@@ -122,4 +122,3 @@ SECTIONS
 }
 
 PROVIDE(_stack = ORIGIN(ram) + LENGTH(ram));
-