arch: um: Fix build for statically linked UML w/ constructors

If CONFIG_CONSTUCTORS is enabled on a statically linked
(CONFIG_STATIC_LINK=y) build of UML, the build fails due to the
.eh_frame section being both used and discarded:

ERROR:root:`.eh_frame' referenced in section `.text' of /usr/lib/gcc/x86_64-linux-gnu/11/crtbeginT.o: defined in discarded section `.eh_frame' of /usr/lib/gcc/x86_64-linux-gnu/11/crtbeginT.o
`.eh_frame' referenced in section `.text' of /usr/lib/gcc/x86_64-linux-gnu/11/crtbeginT.o: defined in discarded section `.eh_frame' of /usr/lib/gcc/x86_64-linux-gnu/11/crtbeginT.o

Instead, keep the .eh_frame section, as we do in dyn.lds.S for
dynamically linked UML.

This can be reproduced with:
./tools/testing/kunit/kunit.py run --kconfig_add CONFIG_STATIC_LINK=y --kconfig_add CONFIG_GCOV_KERNEL=y --kconfig_add CONFIG_DEBUG_FS=y
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/kernel/uml.lds.S

@@ -95,6 +95,7 @@ SECTIONS
   }
 
   .got           : { *(.got.plt) *(.got) }
+  .eh_frame       : { KEEP (*(.eh_frame)) }
   .dynamic       : { *(.dynamic) }
   .tdata	  : { *(.tdata .tdata.* .gnu.linkonce.td.*) }
   .tbss		  : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }