RFR: JDK-8256751: Incremental rebuild with precompiled header fails when touching a header file

[Erik Joelsson]

When building with --disable-absolute-paths-in-output and precompiled header enabled (both of which are default in release builds), then incremental builds of Hotspot fails if a header file is touched.

This is caused by the deps file the compiler generates is now containing relative paths, but those relative paths will not resolve when make imports the file. For all normal compilation units, we post process the file to rewrite these paths to absolute paths, but that call was missed for the precompiled header compilation.

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Commit messages:
 - Fix incremental build of precomp header

Changes: https://git.openjdk.java.net/jdk/pull/1351/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1351&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256751
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1351.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1351/head:pull/1351

PR: https://git.openjdk.java.net/jdk/pull/1351