ppc64le build fixes + ibm-clang

[jstrodtb]

Updated build files for modern ppc64le, including undefining the "vector" macro and supporting ibm-clang. Previously, the ppc64le build would fail to compile.

TYPE: bug fix

KEYWORDS: ppc64le, gcc, build

SOURCE: Joshua Strodtbeck (Tachos High Performance Computing)

DESCRIPTION OF CHANGES: Problem: The old IBM XL compiler has been superseded by ibm-clang. Moreover, both gcc and ibm-clang define a macro called "vector" which causes the preprocessor to fail. Note that this fix depends on islas/cmake-fixSplitCommandFlags, which must be merged first, or the preprocessor fix won't work.

Solution: Added ibm-clang and ppc64le gcc to

ISSUE: For use when this PR closes an issue. N/A

LIST OF MODIFIED FILES: list of changed files (use git diff --name-status master to get formatted list) arch/configure.defaults

TESTS CONDUCTED: Compiled and ran conus2.5km on my Power9 box.

RELEASE NOTE: The latest IBM compiler, ibm-clang, is now supported.