qemu/mcu/arm/stm32.ld: Fix C++ linking.

This commit expands the linkerscript for STM32-series boards to let C++
code link with the interpreter core.

The linkerscript now contains all necessary sections for C++ code that
uses exceptions to be part of a user module inside the MicroPython
image.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>

ports/qemu/mcu/arm/stm32.ld

@@ -19,6 +19,13 @@ SECTIONS
         *(.text*)
         *(.rodata*)
         . = ALIGN(4);
+        *(.ARM.extab*)
+        *(.gnu.linkonce.armextab.*)
+        __exidx_start = .;
+        *(.ARM.exidx*)
+        *(.gnu.linkonce.armexidx.*)
+        __exidx_end = .;
+        . = ALIGN(4);
         _etext = .;
         _sidata = _etext;
     } > ROM