selftests/bpf: Avoid static LLVM linking for cross builds

The BPF selftests prefer static LLVM linking, which works for native
builds but can break cross builds. Its --link-static output may include
host-only libraries that are unavailable for the cross compilation,
causing link failures.

Avoid static LLVM linking for cross builds and use shared LLVM libraries
instead. Native builds keep the existing behavior.

Signed-off-by: Leo Yan <leo.yan@arm.com>

Author: Leo-Yan

tools/testing/selftests/bpf/Makefile

@@ -194,8 +194,15 @@ ifeq ($(feature-llvm),1)
   LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
   # both llvm-config and lib.mk add -D_GNU_SOURCE, which ends up as conflict
   LLVM_CFLAGS  += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags))
-  # Prefer linking statically if it's available, otherwise fallback to shared
-  ifeq ($(shell $(LLVM_CONFIG) --link-static --libs >/dev/null 2>&1 && echo static),static)
+  # Cross compilation must use dynamic linking to avoid unresolved library
+  # dependencies. For native build, prefer linking statically if it's
+  # available, otherwise fallback to shared.
+  ifneq ($(ARCH), $(HOSTARCH))
+    LLVM_LINK_STATIC :=
+  else
+    LLVM_LINK_STATIC := $(shell $(LLVM_CONFIG) --link-static --libs >/dev/null 2>&1 && echo y)
+  endif
+  ifeq ($(LLVM_LINK_STATIC),y)
     LLVM_LDLIBS  += $(shell $(LLVM_CONFIG) --link-static --libs $(LLVM_CONFIG_LIB_COMPONENTS))
     LLVM_LDLIBS  += $(filter-out -lxml2,$(shell $(LLVM_CONFIG) --link-static --system-libs $(LLVM_CONFIG_LIB_COMPONENTS)))
     LLVM_LDLIBS  += -lstdc++