math/octave-forge-interval: fix build on powerpc*

Fixed in LLVM 16:
Assertion failed: ((CGF.CurFuncDecl == nullptr || CGF.Builder.getIsFPConstrained() || isa<CXXConstructorDecl>(CGF.CurFuncDecl) || isa<CXXDestructorDecl>(CGF.CurFuncDecl) || (NewExceptionBehavior == llvm::fp::ebIgnore && NewRoundingBehavior == llvm::RoundingMode::NearestTiesToEven)) && "FPConstrained should be enabled on entire function"), function ConstructorHelper, file /usr/local/poudriere/jails/main-powerpc64/usr/src/contrib/llvm-project/clang/lib/CodeGen/CodeGenFunction.cpp, line 163.
PLEASE submit a bug report to https://bugs.freebsd.org/submit/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: c++ -c -I/usr/local/include/octave-8.2.0 -fPIC -I/usr/local/include/octave-8.2.0/octave/.. -I/usr/local/include/octave-8.2.0/octave -I/usr/local/include -pthread -O2 -pipe -I/usr/local/include/octave-8.2.0 -fstack-protector-strong -fno-strict-aliasing -I/usr/local/include/octave-8.2.0 -Wno-unknown-pragmas __setround__.cc -o /tmp/oct-J3uyET.o
1.	<eof> parser at end of file
2.	Per-file LLVM IR generation
3.	/usr/include/c++/v1/string:1650:10: Generating code for declaration 'std::basic_string<char>::__init'
c++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
FreeBSD clang version 15.0.7 (https://github.com/llvm/llvm-project.git llvmorg-15.0.7-0-g8dfdcc7b7bf6)
Target: powerpc64-unknown-freebsd14.0
Thread model: posix
InstalledDir: /usr/bin

math/octave-forge-interval/Makefile

@@ -16,4 +16,11 @@ LIB_DEPENDS=	libmpfr.so:math/mpfr
 
 USES=		octave
 
+.include <bsd.port.options.mk>
+
+.if ${ARCH:Mpowerpc*}
+CXX=		clang++${LLVM_VERSION}
+USES+=		llvm:min=16
+.endif
+
 .include <bsd.port.mk>