Fixes a clang linking error.

Change-Id: I1d2db53129dc6ec068093ad1e5fc0d94110473b3

vp8/encoder/x86/denoising_sse2.c

diff --git a/vp8/encoder/x86/denoising_sse2.c b/vp8/encoder/x86/denoising_sse2.c
index 34ad916..ee6227f 100644
--- a/vp8/encoder/x86/denoising_sse2.c
+++ b/vp8/encoder/x86/denoising_sse2.c
@@ -22,7 +22,7 @@
     short e[8];
 };
 
-inline int sum_vec_128i(__m128i vec)
+static inline int sum_vec_128i(__m128i vec)
 {
     union sum_union s = { .v = vec };
     return s.e[0] + s.e[1] + s.e[2] + s.e[3] +