Rejig link.x to include more lables to help the linker lay out the objects

Tested with 1.34.0 and 1.38.0 and careful inspection of the linker map
generated on the previously failing
https://github.com/rust-lang/rust/files/3722440/minimal-rust-lld-issue.zip

Closes #188 (I believe)
Closes rust-lang/rust#65391

Signed-off-by: Daniel Egger <daniel@eggers-club.de>

Author: therealprof

cortex-m-rt/link.x.in

@@ -88,29 +88,32 @@ SECTIONS
     *(.text .text.*);
     *(.HardFaultTrampoline);
     *(.HardFault.*);
+    . = ALIGN(4);
+    __etext = .;
   } > FLASH
 
   /* ### .rodata */
-  .rodata : ALIGN(4)
+  .rodata __etext : ALIGN(4)
   {
     *(.rodata .rodata.*);
 
     /* 4-byte align the end (VMA) of this section.
        This is required by LLD to ensure the LMA of the following .data
        section will have the correct alignment. */
     . = ALIGN(4);
+    __erodata = .;
   } > FLASH
 
   /* ## Sections in RAM */
   /* ### .data */
-  .data : ALIGN(4)
+  .data : AT(__erodata) ALIGN(4)
   {
     . = ALIGN(4);
     __sdata = .;
     *(.data .data.*);
     . = ALIGN(4); /* 4-byte align the end (VMA) of this section */
     __edata = .;
-  } > RAM AT > FLASH
+  } > RAM
 
   /* LMA of .data */
   __sidata = LOADADDR(.data);