explicitly label .text sections

nasm should infer .text but does not for windows:
https://bugzilla.nasm.us/show_bug.cgi?id=3392451

Based on libvpx bdbecea

Change-Id: If4f8ecdd7d7ce3e9c5b5286a6422cc954da10d15
diff --git a/aom_dsp/x86/aom_subpixel_bilinear_sse2.asm b/aom_dsp/x86/aom_subpixel_bilinear_sse2.asm
index 8f025a8..57aedcd 100644
--- a/aom_dsp/x86/aom_subpixel_bilinear_sse2.asm
+++ b/aom_dsp/x86/aom_subpixel_bilinear_sse2.asm
@@ -134,6 +134,8 @@
     dec         rcx
 %endm
 
+SECTION .text
+
 global sym(aom_filter_block1d4_v2_sse2) PRIVATE
 sym(aom_filter_block1d4_v2_sse2):
     push        rbp