8168503: JEP 297: Unified arm32/arm64 Port
Reviewed-by: kvn, enevill, ihse, dholmes, erikj, coleenp, cjplummer

8161258: Simplify including platform files.
Summary: Include patform files with macros cpu_header() etc. Do various cleanups of macro usages. Remove _64/_32 from adlc generated files and platform .hpp files. Merge stubRoutines_x86*.hpp. Remove empty mutex_<os>* files.
Reviewed-by: dholmes, coleenp, kbarrett

8156980: Hotspot build doesn't have -std=gnu++98 gcc option
8157358: Syntax error in TOOLCHAIN_CHECK_COMPILER_VERSION
Summary: Add flags for GCC 6 to JVM_CFLAGS and fix prefix handling
Reviewed-by: erikj, kbarrett

8150601: Remove the old Hotspot build system
Reviewed-by: ihse