There is a build failure in aarch64-port/jdk8u-shenandoah when both --enable-jfr and --disable-precompiled-headers are supplied.

.../hotspot/src/share/vm/jfr/writers/jfrEncoders.hpp: In static member function 'static size_t BigEndianEncoderImpl::encode(T, u1*)':
.../hotspot/src/share/vm/jfr/writers/jfrEncoders.hpp:91:8: error: 'Bytes' has not been declared
        Bytes::put_Java_u2(dest, value);
        ^~~~~
.../build/hotspot/src/share/vm/jfr/writers/jfrEncoders.hpp:95:8: error: 'Bytes' has not been declared
        Bytes::put_Java_u4(dest, value);
        ^~~~~
.../hotspot/src/share/vm/jfr/writers/jfrEncoders.hpp:99:8: error: 'Bytes' has not been declared
        Bytes::put_Java_u8(dest, value);
        ^~~~~

Another one is is Shenandoah-specific, already fixed in shenandoah/jdk8 repo, and would come with the merge.
  https://mail.openjdk.java.net/pipermail/shenandoah-dev/2020-June/012413.html
  https://hg.openjdk.java.net/shenandoah/jdk8/hotspot/rev/e16a3f855bf3