av1_dct_test: fix duplicate symbol link error

only expose the static functions needed in the test file to avoid link
errors for e.g., av1_fht4x4_c

Change-Id: I35111d322f30bc2bfc57b32c11f691f0717cfaba

av1/encoder/dct.c

@@ -725,6 +725,8 @@ static void fdct32(const tran_low_t *input, tran_low_t *output) {
   range_check(output, 32, 18);
 }
 
+#ifndef AV1_DCT_GTEST
+
 static void fadst4(const tran_low_t *input, tran_low_t *output) {
   tran_high_t x0, x1, x2, x3;
   tran_high_t s0, s1, s2, s3, s4, s5, s6, s7;
@@ -2223,3 +2225,4 @@ void av1_highbd_fht64x64_c(const int16_t *input, tran_low_t *output, int stride,
 }
 #endif  // CONFIG_TX64X64
 #endif  // CONFIG_AOM_HIGHBITDEPTH
+#endif  // !AV1_DCT_GTEST

test/av1_dct_test.cc

@@ -21,6 +21,7 @@
 
 #undef CONFIG_COEFFICIENT_RANGE_CHECKING
 #define CONFIG_COEFFICIENT_RANGE_CHECKING 1
+#define AV1_DCT_GTEST
 #include "av1/encoder/dct.c"
 
 using libaom_test::ACMRandom;