RFR: 8253891: Debug x86_32 builds fail after JDK-8239090

[Aleksey Shipilev]

`CPU_MAX_FEATURE` is actually a `uint64_t`, with at least 46 bits set. `exact_log2` expects `intptr_t`. The implicit
conversion works on 64-bit, but fails on 32-bit. Calling to `exact_log2_long` seems to cater for both bitnesses.

Testing:
  - [x] tier1 on Linux x86_64
  - [x] tier1 on Linux x86_32 (some unrelated failures)

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Commit messages:
 - 8253891: Debug x86_32 builds fail after JDK-8239090

Changes: https://git.openjdk.java.net/jdk/pull/455/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=455&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253891
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/455.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/455/head:pull/455

PR: https://git.openjdk.java.net/jdk/pull/455