objtool: Hide unnecessary compiler error message

The check for using old libelf prints an error message when libelf.h is
not available but does not abort. This may confuse so hide the compiler
error message.

Signed-off-by: David Engraf <david.engraf@sysgo.com>
Link: https://lore.kernel.org/r/20250203073610.206000-1-david.engraf@sysgo.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Author: dengraf

tools/objtool/Makefile

@@ -37,7 +37,7 @@ OBJTOOL_CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBE
 OBJTOOL_LDFLAGS := $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
 
 # Allow old libelf to be used:
-elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(HOSTCC) $(OBJTOOL_CFLAGS) -x c -E - | grep elf_getshdr)
+elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(HOSTCC) $(OBJTOOL_CFLAGS) -x c -E - 2>/dev/null | grep elf_getshdr)
 OBJTOOL_CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
 
 # Always want host compilation.