https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended-Asm says

  asm [volatile] ( AssemblerTemplate : [OutputOperands] [ : [InputOperands] [ : [Clobbers] ] ] )

which implies that Clobbers is optional even after the third colon, but 
the gcc used for b2g_try_emulator_dep builds says

resample_neon.c: In function 'saturate_32bit_to_16bit':
resample_neon.c:50: error: expected string literal before ')' token

diff --git a/media/libspeex_resampler/src/resample_neon.c b/media/libspeex_resampler/src/resample_neon.c
--- a/media/libspeex_resampler/src/resample_neon.c
+++ b/media/libspeex_resampler/src/resample_neon.c
@@ -56,12 +56,11 @@
 #elif defined(__thumb2__)
 static inline int32_t saturate_32bit_to_16bit(int32_t a) {
     int32_t ret;
     asm ("ssat %[ret], #16, %[a]"
          : [ret] "=r" (ret)
-         : [a] "r" (a)
-         : );
+         : [a] "r" (a));
     return ret;
 }
 #else
 static inline int32_t saturate_32bit_to_16bit(int32_t a) {
     int32_t ret;