selftests/bpf: Use common CFLAGS for urandom_read

The urandom_read helper and its shared library are built with $(CLANG)
directly rather than through the normal selftest $(CC) rules.

The CFLAGS variable can contain specific flags only for $(CC) but might
be imcompatible for $(CLANG) and those flags are not necessarily valid
for the clang-only urandom_read build.

Split the BPF selftest local flags into COMMON_CFLAGS and append them to
CFLAGS for the normal build path. Use COMMON_CFLAGS directly for
urandom_read and liburandom_read.so, while still filtering out -static as
before.

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

Author: Leo-Yan

tools/testing/selftests/bpf/Makefile

@@ -57,7 +57,7 @@ srctree := $(patsubst %/,%,$(dir $(srctree)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
 endif
 
-CFLAGS += -g $(OPT_FLAGS) -rdynamic -std=gnu11				\
+COMMON_CFLAGS = -g $(OPT_FLAGS) -rdynamic -std=gnu11				\
 	  -Wall -Werror -fno-omit-frame-pointer				\
 	  -Wno-unused-but-set-variable					\
 	  $(GENFLAGS) $(SAN_CFLAGS) $(LIBELF_CFLAGS)			\
@@ -70,7 +70,7 @@ LDLIBS += $(LIBELF_LIBS) -lz -lrt -lpthread
 PCAP_CFLAGS	:= $(shell $(PKG_CONFIG) --cflags libpcap 2>/dev/null && echo "-DTRAFFIC_MONITOR=1")
 PCAP_LIBS	:= $(shell $(PKG_CONFIG) --libs libpcap 2>/dev/null)
 LDLIBS += $(PCAP_LIBS)
-CFLAGS += $(PCAP_CFLAGS)
+CFLAGS += $(COMMON_CFLAGS) $(PCAP_CFLAGS)
 
 # Some utility functions use LLVM libraries
 jit_disasm_helpers.c-CFLAGS = $(LLVM_CFLAGS)
@@ -267,7 +267,7 @@ endif
 $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom_read.map
 	$(call msg,LIB,,$@)
 	$(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
-		     $(filter-out -static,$(CFLAGS) $(LDFLAGS)) \
+		     $(filter-out -static,$(COMMON_CFLAGS) $(LDFLAGS)) \
 		     $(filter %.c,$^) $(filter-out -static,$(LDLIBS)) \
 		     -Wno-unused-command-line-argument \
 		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
@@ -277,7 +277,7 @@ $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom
 $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_read.so
 	$(call msg,BINARY,,$@)
 	$(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
-		     $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
+		     $(filter-out -static,$(COMMON_CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
 		     -Wno-unused-command-line-argument \
 		     -lurandom_read $(filter-out -static,$(LDLIBS)) -L$(OUTPUT) \
 		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \