RFR: 8345744: Use C++ LINK_TYPE with SetupBuildLauncher in StaticLibs.gmk

[Jiangli Zhou]

Please review following fix for linking static JDK launcher, thanks.

- Set LINK_TYPE to C++ when building the static launcher to make sure LDCXX instead of LD is used for linking.

- Remove -l:libstdc++. For linux, -static-libstdc++ is already set in STATIC_STDCXX_FLAGS. See https://github.com/openjdk/jdk/blob/e0d639878346946d0627a57b0eeb0cac8ca533fc/make/autoconf/lib-std.m4#L50.

See more details in https://bugs.openjdk.org/browse/JDK-8345744.

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Commit messages:
 - - Set LINK_TYPE to C++ when building the static launcher to make sure LDCXX instead of LD is used for linking.

Changes: https://git.openjdk.org/jdk/pull/22624/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22624&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345744
  Stats: 3 lines in 2 files changed: 2 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22624.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22624/head:pull/22624

PR: https://git.openjdk.org/jdk/pull/22624