docs/misra: document gcc-specific behavior with shifting signed integers

Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

docs/misra/C-language-toolchain.rst

@@ -200,6 +200,15 @@ The table columns are as follows:
      - ARM64, X86_64
      - See Section "6.29 Designated Initializers" of GCC_MANUAL
 
+   * - Signed << compiler-defined behavior
+     - All architectures
+     - See Section "4.5 Integers" of GCC_MANUAL. As an extension to the
+       C language, GCC does not use the latitude given in C99 and C11
+       only to treat certain aspects of signed << as undefined.
+
+   * - Signed >> acts on negative numbers by sign extension
+     - All architectures
+     - See Section "4.5 Integers" of GCC_MANUAL.
 
 Translation Limits
 __________________