Applying ./patches/01-Makefile.patch using plaintext: 
patching file Makefile
make[3]: Entering directory '/mnt/immortalwrt-18.06/build_dir/target-mipsel_24kc+24kf_musl/asterisk-opus-2017-10-09-83e1b458'
ccache_cc -o codecs/codec_opus_open_source.so  -DAST_MODULE=\"codec_opus_open_source\"  -Os -pipe -mno-branch-likely -mips32r2 -mtune=24kc -fno-caller-saves -fno-plt -fhonour-copts -Wno-error=unused-but-set-variable -Wno-error=unused-result -mips16 -minterlink-mips16 -ffile-prefix-map=/mnt/immortalwrt-18.06/build_dir/target-mipsel_24kc+24kf_musl/asterisk-opus-2017-10-09-83e1b458=asterisk-opus-2017-10-09-83e1b458 -Wformat -Werror=format-security -fstack-protector -D_FORTIFY_SOURCE=1 -Wl,-z,now -Wl,-z,relro -DAST_MODULE_SELF_SYM=__internal_codec_opus_open_source_self -DPIC -fpic  -I/mnt/immortalwrt-18.06/staging_dir/toolchain-mipsel_24kc+24kf_gcc-8.4.0_musl/usr/include -I/mnt/immortalwrt-18.06/staging_dir/toolchain-mipsel_24kc+24kf_gcc-8.4.0_musl/include/fortify -I/mnt/immortalwrt-18.06/staging_dir/toolchain-mipsel_24kc+24kf_gcc-8.4.0_musl/include  -pthread -lopus -L/mnt/immortalwrt-18.06/staging_dir/toolchain-mipsel_24kc+24kf_gcc-8.4.0_musl/usr/lib -L/mnt/immortalwrt-18.06/staging_dir/toolchain-mipsel_24kc+24kf_gcc-8.4.0_musl/lib -znow -zrelro  -shared -pthread -Wl,--warn-common codecs/codec_opus_open_source.c
codecs/codec_opus_open_source.c:39:10: fatal error: asterisk.h: No such file or directory
 #include "asterisk.h"
          ^~~~~~~~~~~~
compilation terminated.
make[3]: *** [Makefile:50: codecs/codec_opus_open_source.so] Error 1
make[3]: Leaving directory '/mnt/immortalwrt-18.06/build_dir/target-mipsel_24kc+24kf_musl/asterisk-opus-2017-10-09-83e1b458'
make[2]: *** [Makefile:64: /mnt/immortalwrt-18.06/build_dir/target-mipsel_24kc+24kf_musl/asterisk-opus-2017-10-09-83e1b458/.built] Error 2
time: package/feeds/telephony/asterisk-opus/compile#0.12#0.02#0.21