remove failure if libiberty cannot be found

meson.build

@@ -575,8 +575,6 @@ elif compiler.has_header('libiberty/libiberty.h',
                          include_directories: include_directories(incdirs))
     # Debian and derivatives e.g. Ubuntu
     cflags += '-D__HAVE_LIBIBERTY_LIBIBERTYH__'
-else
-    error('cannot find libiberty.h at either <libiberty.h> or <libiberty/libiberty.h>')
 endif
 
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