RFR: Make Loom buildable on x86_32 [v3]

[Aleksey Shipilev]

> This PRs make Loom workspace at least buildable on x86_32. 
> 
> Since jlink/jmod run build JDK, the JDK itself has to start well, without touching Loom code. Current patch only does `make images` well, trying to run `tier1` with `x86_32` quickly fails with multiple errors -- I suspect deopt, G1 and other changes are subtly broken on x86_32. I shall continue the fixes in another PR, and this push would unhoard the generic 32-bit fixes in format specifiers.
> 
> Additional testing:
>  - [x] 10x `CONF=linux-x86-server-fastdebug make clean-images images`

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Fix another register clash on x86_32 (rcx is used later as rthread)
 - Merge branch 'fibers' into basic-x86-32-builds
 - Merge branch 'fibers' into basic-x86-32-builds
 - More accurate register saving
 - More precise post_call_nops
 - Select the register better
 - Linux x86_32 builds fine

-------------

Changes:
  - all: https://git.openjdk.java.net/loom/pull/65/files
  - new: https://git.openjdk.java.net/loom/pull/65/files/db6a87ae..2d420624

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=65&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=65&range=01-02

  Stats: 2866 lines in 136 files changed: 385 ins; 2202 del; 279 mod
  Patch: https://git.openjdk.java.net/loom/pull/65.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/65/head:pull/65

PR: https://git.openjdk.java.net/loom/pull/65