Use -Wno-vla-cxx-extension for libomp, since clang 18 complains.

Author: DimitryAndric

lib/libomp/Makefile

@@ -57,7 +57,8 @@ CXXFLAGS+=	-fno-exceptions
 CXXFLAGS+=	-fno-rtti
 CXXSTD=		c++17
 
-.if ${COMPILER_TYPE} == "clang" && ${MACHINE_CPUARCH} == "i386"
+.if ${COMPILER_TYPE} == "clang"
+.if ${MACHINE_CPUARCH} == "i386"
 .if ${COMPILER_VERSION} >= 90000
 # When targeting i386, clang 9.0.0 produces a new warning about large atomic
 # operations "possibly incurring significant performance penalties", but there
@@ -69,8 +70,14 @@ CWARNFLAGS+=	-Wno-atomic-alignment
 # builtin operations must have natural alignment, but there is not much we
 # can do about it.
 CWARNFLAGS+=	-Wno-sync-alignment
-.endif
-.endif
+.endif # COMPILER_VERSION >= 170000
+.endif # MACHINE_CPUARCH == i386
+.if ${COMPILER_VERSION} >= 180000
+# clang 18.0.0 introduces a new warning about variable length arrays in C++,
+# which OpenMP makes use of in several sources.
+CXXWARNFLAGS+=	-Wno-vla-cxx-extension
+.endif # COMPILER_VERSION >= 180000
+.endif # COMPILER_TYPE == clang
 
 LDFLAGS+=	-Wl,--warn-shared-textrel
 LDFLAGS+=	-Wl,--gc-sections