[LTP] [PATCH] Add __clear_cache declaration for clang

[Khem Raj]

__clear_cache was enabled on RISCV recently with 7352ba02390116f1cd6a9b583860ba28aa0a1b7a
however it fails to compile with clang19 on RISCV
With this error

  hugemmap15.c:51:2: error: call to undeclared function '__clear_cache'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
      51 |         __clear_cache(p, p + COPY_SIZE);
         |         ^

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Hui Min Mina Chou <minachou@andestech.com>
---
 testcases/kernel/mem/hugetlb/hugemmap/hugemmap15.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap15.c b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap15.c
index a84ba6476..856e22ff3 100644
--- a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap15.c
+++ b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap15.c
@@ -21,6 +21,7 @@
 
 #if defined(__clang__)
 	#pragma clang optimize off
+	void __clear_cache(void *start, void *end);
 #endif
 
 #define _GNU_SOURCE