I changed GCC toolchain from GCC6 to GCC8 on SLES12SP5 Linux s390x.
I could see following errors:
======
src/java.desktop/share/native/libawt/awt/medialib/awt_ImagingLib.c: In function 'allocateRasterArray':
src/java.desktop/share/native/libawt/awt/medialib/awt_ImagingLib.c:2944:73: error: 'roff[3]' may be used uninitialized in this function [-Werror=maybe-uninitialized]
                             (((*inP&rasterP->sppsm.maskArray[c]) >> roff[c])
                                                                     ~~~~^~~
======

According to error messages,
roff and loff may not be initialized.

GCC8 is:
======
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib64/gcc/s390x-suse-linux/8/lto-wrapper
Target: s390x-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info --mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64 --enable-languages=c,c++,objc,fortran,obj-c++,go --enable-checking=release --disable-werror --with-gxx-include-dir=/usr/include/c++/8 --enable-ssp --disable-libssp --disable-libvtv --disable-libmpx --disable-cet --disable-libcc1 --disable-plugin --with-bugurl=http://bugs.opensuse.org/ --with-pkgversion='SUSE Linux' --with-slibdir=/lib64 --with-system-zlib --enable-__cxa_atexit --enable-libstdcxx-allocator=new --disable-libstdcxx-pch --with-default-libstdcxx-abi=gcc4-compatible --enable-version-specific-runtime-libs --with-gcc-major-version-only --enable-linker-build-id --enable-linux-futex --enable-gnu-indirect-function --program-suffix=-8 --without-system-libunwind --with-tune=zEC12 --with-arch=z196 --with-long-double-128 --enable-decimal-float --build=s390x-suse-linux --host=s390x-suse-linux
Thread model: posix
gcc version 8.2.1 20180831 [gcc-8-branch revision 264010] (SUSE Linux)
======