Tvheadend won't compile with "full language support"

Hello.
I'm using master branch with WRT1900ACv1. If I select "Global build settings" / "Compile with full language support", tvheadend package won't compile. The error is:

ccache_cc -MD -MP -O3 -pipe -fno-caller-saves -fno-plt -fhonour-copts -Wno-error=unused-but-set-variable -Wno-error=unused-result -mfloat-abi=hard -fmacro-prefix-map=/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10=tvheadend-4.0.10 -I/build/openwrt0/staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/lib/libiconv-full/include -I/build/openwrt0/staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/lib/libintl-full/include  -I/build/openwrt0/staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/usr/include -I/build/openwrt0/staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify -I/build/openwrt0/staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include -I/build/openwrt0/staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/lib/libiconv-full/include -I/build/openwrt0/staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/lib/libintl-full/include  -O3 -pipe -fno-caller-saves -fno-plt -fhonour-copts -Wno-error=unused-but-set-variable -Wno-error=unused-result -mfloat-abi=hard -fmacro-prefix-map=/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10=tvheadend-4.0.10 -Wformat -Werror=format-security -fstack-protector-strong -D_FORTIFY_SOURCE=1 -Wl,-z,now -Wl,-z,relro -I/build/openwrt0/staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/lib/libiconv-full/include -I/build/openwrt0/staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/lib/libintl-full/include  -I/build/openwrt0/staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/include  -I/build/openwrt0/staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/include  -g -O2 -Wunused-result -Wmissing-prototypes -fms-extensions -funsigned-char -fno-strict-aliasing -D_FILE_OFFSET_BITS=64 -I/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10/build.linux -I/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10/src -I/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10 -I/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10/libhdhomerun_static -c -o /build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10/build.linux/src/intlconv.o src/intlconv.c
cc1: note: someone does not honour COPTS correctly, passed 2 times
In file included from ../../../staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify/strings.h:22,
                 from /build/openwrt0/staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/string.h:57,
                 from ../../../staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify/wchar.h:30,
                 from ../../../staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/lib/libiconv-full/include/iconv.h:110,
                 from src/intlconv.c:1:
../../../staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify/string.h:144:13: error: 'mempcpy' undeclared here (not in a function); did you mean 'memccpy'?
  144 | _FORTIFY_FN(mempcpy) void *mempcpy(void *__d, const void *__s, size_t __n)
      |             ^~~~~~~
In file included from src/tvheadend.h:31,
                 from src/intlconv.c:2:
../../../staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify/string.h: In function 'mempcpy':
../../../staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify/string.h:151:9: error: called object '__orig_mempcpy' is not a function or function pointer
  151 |  return __orig_mempcpy(__d, __s, __n);
      |         ^~~~~~~~~~~~~~
In file included from ../../../staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify/strings.h:22,
                 from /build/openwrt0/staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/string.h:57,
                 from ../../../staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify/wchar.h:30,
                 from ../../../staging_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/usr/lib/libiconv-full/include/iconv.h:110,
                 from src/intlconv.c:1:
../../../staging_dir/toolchain-arm_cortex-a9+vfpv3-d16_gcc-10.2.0_musl_eabi/include/fortify/string.h:144:1: note: declared here
  144 | _FORTIFY_FN(mempcpy) void *mempcpy(void *__d, const void *__s, size_t __n)
      | ^~~~~~~~~~~
Makefile:441: recipe for target '/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10/build.linux/src/intlconv.o' failed
make[4]: *** [/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10/build.linux/src/intlconv.o] Error 1
make[4]: Leaving directory '/build/openwrt0/build_dir/target-arm_cortex-a9+vfpv3-d16_musl_eabi/tvheadend-4.0.10'

I selected "full language support" especially for tvheadend: TV program names and descriptions are written in various languages and I want unicode characters to show properly.