clang and -DINCLUDE_SUFFIX_COMPILER=_gcc -DTARGET_COMPILER_gcc

[Martin Buchholz]

I saw in the *.cmdline files that when I build with clang, we get these
defines:
 -DINCLUDE_SUFFIX_COMPILER=_gcc -DTARGET_COMPILER_gcc

I see now that -DTARGET_COMPILER_gcc was intentional

  HOTSPOT_TOOLCHAIN_TYPE=$TOOLCHAIN_TYPE
  if test "x$TOOLCHAIN_TYPE" = xclang; then
    HOTSPOT_TOOLCHAIN_TYPE=gcc

but it's very confusing and isn't used in too many places, so should be
fixed.