Several parts of the make system in the JDK has large parts of cluttered if branches dedicated to setting flags for the specific compiler used in the build. This could be more neatly accomplished by instead adding more target combinations in SetupNativeCompilation so the callsite can more cleanly specify which OS and compiler it desires to set these flags for. The proposed change includes several combinations as follows:

DISABLED_WARNINGS, CFLAGS/CXXFLAGS and LDFLAGS: Compiler-then-OS (The priority shown reflects how the flags depend more so on the compiler)
LIBS: OS-then-Compiler, as libraries typically vary based on the system being compiled for