corrects spelling in linker file to adhere to convention

src/sections.ld

@@ -97,7 +97,7 @@ SECTIONS
   /* stack segement, PHDR is stack */
   .stack ORIGIN(LOCATION_STACK) + LENGTH(LOCATION_STACK) - __stack_segment_size :
   {
-    PROVIDE( _heap_end = . );
+    PROVIDE( __heap_end = . );
     . = __stack_segment_size;
     PROVIDE( _sp = . );
   } >LOCATION_STACK AT>LOCATION_STACK 
@@ -105,5 +105,13 @@ SECTIONS
   PROVIDE( tohost = . );
   PROVIDE( fromhost = . + 8 );
 
+  .trace_buffer (NOLOAD) :
+  {
+    . =  ORIGIN(trace);
+    __trace_buffer_start = .;
+    . = ORIGIN(trace) + LENGTH(trace);  /* pad until end of trace */
+    __trace_buffer_end = .;
+  } > trace
+
   /DISCARD/ : { *(.eh_frame*) *(.comment) *(.note .note.*) }
 }