Modularize JVM flags declaration

The purpose of this RFE is to improve modularization of the source code and speed up compilation of HotSpot C++ source code.

Today all global variables generated by the JVM XXX_FLAGS macros are declared at the end of globals.hpp.

http://hg.openjdk.java.net/jdk/jdk/file/4a5a7dc9d05c/src/hotspot/share/runtime/globals.hpp#l2498

As a result, any file that needs just one of such globals will need to include a large number of header files, with a total of over 1000 global declarations.

We should modularize this by doing the variable declaration in each individual header that has a XXX_FLAGS specification. E.g.,

c1_globals.hpp:

    #define C1_FLAGS(develop, develop_pd, product, .........) \
        develop(intx, C1FlagA, 123, "some flag A for C1) \
        product(intx, C1FlagB, 456, "some flag B for C1)
   DECLARE_FLAGS(C1_FLAGS)

The DECLARE_FLAGS macro will expand to this (in product build)
    extern intx C1FlagA;
    const intx C1FlagB = 456;

Most of the HotSpot files that reference C1FlagA/C1FlagB can simply include c1_globals.hpp, without including the other unrelated xxx_globals.hpp file.

DECLARE_FLAGS would be something like:

#define DECLARE_FLAGS(FLAG_SPECIFIER) \
    FLAG_SPECIFIER(
          DECLARE_DEVELOPER_FLAG, \
          DECLARE_PD_DEVELOPER_FLAG, \
          DECLARE_PRODUCT_FLAG, \
          DECLARE_PD_PRODUCT_FLAG, \
          DECLARE_NOTPRODUCT_FLAG, \
          IGNORE_RANGE, \
          IGNORE_CONSTRAINT)