RFR: Make Loom buildable on x86_32

[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`

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Commit messages:
 - More accurate register saving
 - More precise post_call_nops
 - Select the register better
 - Linux x86_32 builds fine

Changes: https://git.openjdk.java.net/loom/pull/65/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=65&range=00
  Stats: 115 lines in 15 files changed: 63 ins; 3 del; 49 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