RFR: 8331167: UBSan enabled build fails in adlc on macOS

[Matthias Baesken]

When configuring with '--enable-ubsan' (https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html) and doing a macOS x86_64 fastdebug build, I run into this build error after very short time :
jdk/src/hotspot/share/adlc/adlparse.cpp:5228:36: runtime error: applying non-zero offset 1 to null pointer
    #0 0x103fa4b4b in ADLParser::skipws_common(bool) adlparse.cpp:5228
    #1 0x103f76aed in ADLParser::skipws() adlparse.hpp:271
    #2 0x103f763c6 in ADLParser::parse() adlparse.cpp:95
    #3 0x10407054d in main main.cpp:178
    #4 0x7fff2044ef3c in start+0x0 (libdyld.dylib:x86_64+0x15f3c)

So it seems that UBSan support is currently not working well on macOS because the build fails early.  Seems we add 1 to a nullptr in the adlc code in some cases and UBSAN complains about it.

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Commit messages:
 - JDK-8331167

Changes: https://git.openjdk.org/jdk/pull/18976/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18976&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331167
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18976.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18976/head:pull/18976

PR: https://git.openjdk.org/jdk/pull/18976