docs: update the known issues

docs/known-issues.txt

@@ -80,3 +80,20 @@ Workaround:
   Disable the cross-ldd build.
 
 --------------------------------
+Symptoms:
+  On 64-bit build systems, the glibc (possibly eglibc too) build fails for
+  64-bit targets, because it can not find libgcc.
+
+Explanations:
+  This issue has been observed when the companion libraries are built
+  statically. For an unknown reason, in this case, the libgcc built by the
+  core gcc is not located in the same place it is located when building
+  with shared companion libraries.
+
+Fix:
+  None so far.
+
+Workaround:
+  Build shared companion libraries.
+
+--------------------------------