Automake error on openwrt 18.06 compile

Hi

I am compiling OpenWrt 18.06.8 on Ubuntu 18. I received the following error:

lib/Automake/Config.pm-t; then echo "lib/Automake/Config.pm contains unexpanded substitution (see lines above)"; exit 1; fi; chmod a-w lib/Automake/Config.pm-t && mv -f lib/Automake/Config.pm-t lib/Automake/Config.pm
: && /bin/mkdir -p doc && { PATH='/home/ubuntu/openwrt/build_dir/target-mips_24kc_musl/automake-1.15/t/wrap:'$PATH && export PATH; } && /home/ubuntu/openwrt/staging_dir/host/bin/perl ./doc/help2man --output=doc/aclocal-1.15.1 aclocal-1.15
: && /bin/mkdir -p doc && { PATH='/home/ubuntu/openwrt/build_dir/target-mips_24kc_musl/automake-1.15/t/wrap:'$PATH && export PATH; } && /home/ubuntu/openwrt/staging_dir/host/bin/perl ./doc/help2man --output=doc/automake-1.15.1 automake-1.15
help2man: can't get `--help' info from automake-1.15
Try `--no-discard-stderr' if option outputs to stderr
Makefile:3687: recipe for target 'doc/automake-1.15.1' failed
make[4]: *** [doc/automake-1.15.1] Error 255
make[4]: Leaving directory '/home/ubuntu/openwrt/build_dir/target-mips_24kc_musl/automake-1.15'
Makefile:65: recipe for target '/home/ubuntu/openwrt/build_dir/target-mips_24kc_musl/automake-1.15/.built' failed
make[3]: *** [/home/ubuntu/openwrt/build_dir/target-mips_24kc_musl/automake-1.15/.built] Error 2
make[3]: Leaving directory '/home/ubuntu/openwrt/feeds/packages/devel/automake'
time: package/feeds/packages/automake/compile#2.98#1.05#9.39
package/Makefile:111: recipe for target 'package/feeds/packages/automake/compile' failed
make[2]: *** [package/feeds/packages/automake/compile] Error 2
make[2]: Leaving directory '/home/ubuntu/openwrt'
package/Makefile:107: recipe for target '/home/ubuntu/openwrt/staging_dir/target-mips_24kc_musl/stamp/.package_compile' failed
make[1]: *** [/home/ubuntu/openwrt/staging_dir/target-mips_24kc_musl/stamp/.package_compile] Error 2
make[1]: Leaving directory '/home/ubuntu/openwrt'
/home/ubuntu/openwrt/include/toplevel.mk:216: recipe for target 'world' failed
make: *** [world] Error 2

I found if I add "--no-discard-stderr" to line 3687 on openwrt/build_dir/target-mips_24kc_musl/automake-1.15/Makefile, then I can succefully make it locally. But when I run the global openWrt make, this file will be rewritten.

Is there any solution for this issue and how/where can I modify the automake source file?