RFR: 8285850 : [AIX] unreachable code in basic_tools.m4 -> BASIC_CHECK_TAR

[Deepa Kumari]

basic_tools.m4 contains the line 'elif test "x$TAR_TYPE" = "aix";...' The comparison "x$TAR_TYPE" = "aix" can never be true. Adding an 'x' to both sides of the comparison prevents an erroneous match when the variable is the empty string.

Verified the test after successful build and reflecting changes 'elif test "x$TAR_TYPE" = "xaix";...' on generated-configure.sh file.

Reported Issue : [JDK-8285850](https://bugs.openjdk.org/browse/JDK-8285850)

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Commit messages:
 - 8285850 : [AIX] unreachable code in basic_tools.m4 -> BASIC_CHECK_TAR
 - Modified  LoadedLibraries::reload() in dll_unload os_posix.cpp
 - Added LoadedLibraries::reload() in dll_unload() function in os_posix.cpp
 - Modified LoadedLibraries::print() in loadlib_aix.cpp

Changes: https://git.openjdk.org/jdk/pull/12146/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12146&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8285850
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12146.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12146/head:pull/12146

PR: https://git.openjdk.org/jdk/pull/12146