[foreign-memaccess+abi] RFR: 8266916: Simplify logic for creating libSysLookup

[Maurizio Cimadamore]

On Linux/Mac, the makefile for generating libSysLookup contains some unnecessary flags (given that the sources contain no code).
Moreover, it is not necessary to have a list of all headers - we can just include a single header (to make the build/toolchain happy) and rely on linker to pull in dependencies.
On Linux, also add `libdl` as a dependency (the VM also depends on that, so we can depend on that).

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Commit messages:
 - Initial push

Changes: https://git.openjdk.java.net/panama-foreign/pull/533/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=533&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266916
  Stats: 36 lines in 2 files changed: 0 ins; 33 del; 3 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/533.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/533/head:pull/533

PR: https://git.openjdk.java.net/panama-foreign/pull/533