buildman: Support disabling LTO

This cuts down build performance considerably and is not always needed,
when checking for build errors, etc.

Add a flag to disable it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/builderthread.py b/tools/buildman/builderthread.py
index 7ba9a85..dae3d4a 100644
--- a/tools/buildman/builderthread.py
+++ b/tools/buildman/builderthread.py
@@ -255,6 +255,8 @@
                     args.append('KCFLAGS=-Werror')
                 if self.builder.allow_missing:
                     args.append('BINMAN_ALLOW_MISSING=1')
+                if self.builder.no_lto:
+                    args.append('NO_LTO=1')
                 config_args = ['%s_defconfig' % brd.target]
                 config_out = ''
                 args.extend(self.builder.toolchains.GetMakeArguments(brd))