java issues with building on plain Ubuntu LTS 18.04
I've abandoned the build host that I used successfully in 2019, and spun up an EC2 with Ubuntu 18.04. classpath-0.99 needs a javac. (Why do we need classpath... I don't know). openjdk does not seem to satisfy it. gcj doesn't seem to be a thing on ubuntu. oracle java 11 or 13 seems to be incompatible, so I copied java 8 from my old build server and adjusted /etc/alternatives/javac.... but now I get the following silly warning that becomes an error.
Sigh.
make[7]: Entering directory '/home/ubuntu/turris-build/build/build_dir/target-arm_cortex-a9+vfpv3_musl_eabi/classpath-0.99/native/jni/java-math'
/bin/bash ../../../libtool --tag=CC --mode=compile ccache_cc -DHAVE_CONFIG_H -I. -I../../../include -I../../../include -I../../../native/jni/classpath -I../../../native/jni/native-lib -I/home/ubuntu/turris-build/build/staging_dir/target-arm_cortex-a9+vfpv3_musl_eabi/usr/include -I/home/ubuntu/turris-build/build/staging_dir/target-arm_cortex-a9+vfpv3_musl_eabi/include -I/home/ubuntu/turris-build/build/staging_dir/toolchain-arm_cortex-a9+vfpv3_gcc-7.3.0_musl_eabi/usr/include -I/home/ubuntu/turris-build/build/staging_dir/toolchain-arm_cortex-a9+vfpv3_gcc-7.3.0_musl_eabi/include/fortify -I/home/ubuntu/turris-build/build/staging_dir/toolchain-arm_cortex-a9+vfpv3_gcc-7.3.0_musl_eabi/include -W -Wall -Wmissing-declarations -Wwrite-strings -Wmissing-prototypes -Wno-long-long -Werror -I/home/ubuntu/turris-build/build/staging_dir/target-arm_cortex-a9+vfpv3_musl_eabi/usr/include -Os -pipe -mcpu=cortex-a9 -mfpu=vfpv3-d16 -fno-caller-saves -fno-plt -fhonour-copts -Wno-error=unused-but-set-variable -Wno-error=unused-result -mfloat-abi=hard -iremap/home/ubuntu/turris-build/build/build_dir/target-arm_cortex-a9+vfpv3_musl_eabi/classpath-0.99:classpath-0.99 -Wformat -Werror=format-security -fstack-protector -D_FORTIFY_SOURCE=1 -Wl,-z,now -Wl,-z,relro -MT gnu_java_math_GMP.lo -MD -MP -MF .deps/gnu_java_math_GMP.Tpo -c -o gnu_java_math_GMP.lo gnu_java_math_GMP.c
OpenWrt-libtool: compile: ccache_cc -DHAVE_CONFIG_H -I. -I../../../include -I../../../include -I../../../native/jni/classpath -I../../../native/jni/native-lib -I/home/ubuntu/turris-build/build/staging_dir/target-arm_cortex-a9+vfpv3_musl_eabi/usr/include -I/home/ubuntu/turris-build/build/staging_dir/target-arm_cortex-a9+vfpv3_musl_eabi/include -I/home/ubuntu/turris-build/build/staging_dir/toolchain-arm_cortex-a9+vfpv3_gcc-7.3.0_musl_eabi/usr/include -I/home/ubuntu/turris-build/build/staging_dir/toolchain-arm_cortex-a9+vfpv3_gcc-7.3.0_musl_eabi/include/fortify -I/home/ubuntu/turris-build/build/staging_dir/toolchain-arm_cortex-a9+vfpv3_gcc-7.3.0_musl_eabi/include -W -Wall -Wmissing-declarations -Wwrite-strings -Wmissing-prototypes -Wno-long-long -Werror -I/home/ubuntu/turris-build/build/staging_dir/target-arm_cortex-a9+vfpv3_musl_eabi/usr/include -Os -pipe -mcpu=cortex-a9 -mfpu=vfpv3-d16 -fno-caller-saves -fno-plt -fhonour-copts -Wno-error=unused-but-set-variable -Wno-error=unused-result -mfloat-abi=hard -iremap/home/ubuntu/turris-build/build/build_dir/target-arm_cortex-a9+vfpv3_musl_eabi/classpath-0.99:classpath-0.99 -Wformat -Werror=format-security -fstack-protector -D_FORTIFY_SOURCE=1 -Wl,-z,now -Wl,-z,relro -MT gnu_java_math_GMP.lo -MD -MP -MF .deps/gnu_java_math_GMP.Tpo -c gnu_java_math_GMP.c -fPIC -DPIC -o .libs/gnu_java_math_GMP.o
gnu_java_math_GMP.c: In function 'Java_gnu_java_math_GMP_natSetBitCount':
gnu_java_math_GMP.c:1134:13: error: this statement may fall through [-Werror=implicit-fallthrough=]
res = mpz_popcount (_this);
~~~~^~~~~~~~~~~~~~~~~~~~~~
gnu_java_math_GMP.c:1135:7: note: here
default:
^~~~~~~
cc1: all warnings being treated as errors
Makefile:531: recipe for target 'gnu_java_math_GMP.lo' failed
make[7]: *** [gnu_java_math_GMP.lo] Error 1
make[7]: Leaving directory '/home/ubuntu/turris-build/build/build_dir/target-arm_cortex-a9+vfpv3_musl_eabi/classpath-0.99/native/jni/java-math'
Makefile:469: recipe for target 'all-recursive' failed
make[6]: *** [all-recursive] Error 1
make[6]: Leaving directory '/home/ubuntu/turris-build/build/build_dir/target-arm_cortex-a9+vfpv3_musl_eabi/classpath-0.99/native/jni'
Makefile:457: recipe for target 'all-recursive' failed
make[5]: *** [all-recursive] Error 1
make[5]: Leaving directory '/home/ubuntu/turris-build/build/build_dir/target-arm_cortex-a9+vfpv3_musl_eabi/classpath-0.99/native'
Makefile:516: recipe for target 'all-recursive' failed
make[4]: *** [all-recursive] Error 1