[PATCH 2/2] selftests/sched_ext: Move -rdynamic to LDFLAGS and append to it

[Cheng-Yang Chou <yphbchou0911@gmail.com>]

CFLAGS passes the link-time flag -rdynamic to compile steps ($(CC) -c),
where it is unused. Under -Werror, Clang fails the build:

    $ make CC=clang-21
    clang-21: error: argument unused during compilation: '-rdynamic'
                     [-Werror,-Wunused-command-line-argument]

Unlike the demo schedulers, the selftest runner requires -rdynamic at
link time to populate .dynsym for testcases. Additionally, LDFLAGS uses
'=' rather than '+=', silently discarding USERLDFLAGS from lib.mk.

Move -rdynamic from CFLAGS to LDFLAGS and append with '+='. This fixes
builds with CC=clang-N while preserving symbol export and USERLDFLAGS.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/testing/selftests/sched_ext/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index 3cfe90e0f34fa..c756285a4903e 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -53,7 +53,7 @@ ifneq ($(wildcard $(GENHDR)),)
   GENFLAGS := -DHAVE_GENHDR
 endif
 
-CFLAGS += -g -O2 -rdynamic -pthread -Wall -Werror $(GENFLAGS)			\
+CFLAGS += -g -O2 -pthread -Wall -Werror $(GENFLAGS)				\
 	  -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)				\
 	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(CURDIR)/include -I$(SCXTOOLSINCDIR)
 
@@ -62,7 +62,7 @@ ifneq ($(LLVM),)
 CFLAGS += -Wno-unused-command-line-argument
 endif
 
-LDFLAGS = -lelf -lz -lpthread -lzstd
+LDFLAGS += -rdynamic -lelf -lz -lpthread -lzstd
 
 IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null |				\
 			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
-- 
2.43.0