6816311 fix broke solaris builds when ALT_JDK_DEVTOOLS was used (used by RE).

When ALT_JDK_DEVTOOLS is used the COMPILER_PATH was being defined using the value of COMPILER_VERSION, but the changes in 6816311 made the COMPILER_NAME and COMPILER_VERSION (what is being used) defined via CC_VER (set with cc -version), but CC_VER dependeded on COMPILER_PATH. :^( Horrible cycle of make variable usage.

1. The use of COMPILER_VERSION in COMPILER_PATH really should be REQUIRED_COMPILER_VERSION.

2. The Defs-versions.gmk file that defines the REQUIRED* variables, needs to be included before the Compiler*.gmk files and after CC_VERSION is defined. (The names of all these CC*VER* variables should probably be re-organized.)