java/openjdk11: respect compiler and linker flags

pass CFLAGS, CXXFLAGS and LDFLAGS to the build
This enables more easily testing different build options.

fix build on gcc by passing --disable-precompiled-headers not only on powerpc64
"Without this, I was getting PCH-error from g++12 on my amd64 machine too."

PR: 279367
Tested by: poudriere
Approved by: maintainer timeout (java@)