If you're trying to build AOSP on Mac High Sierra and getting this (or a similar error):

[  0% 35/75651] yacc out/soong/.intermediates/system/tools/aidl/libaidl-common/darwin_x86_64_static/gen/yacc/system/tools/aidl/aidl_language_y.cpp
FAILED: out/soong/.intermediates/system/tools/aidl/libaidl-common/darwin_x86_64_static/gen/yacc/system/tools/aidl/aidl_language_y.cpp out/soong/.intermediates/system/tools/aidl/libaidl-common/darwin_x86_64_static/gen/yacc/system/tools/aidl/aidl_language_y.h  
BISON_PKGDATADIR=external/bison/data prebuilts/misc/darwin-x86/bison/bison -d  --defines=out/soong/.intermediates/system/tools/aidl/libaidl-common/darwin_x86_64_static/gen/yacc/system/tools/aidl/aidl_language_y.h -o out/soong/.intermediates/system/tools/aidl/libaidl-common/darwin_x86_64_static/gen/yacc/system/tools/aidl/aidl_language_y.cpp system/tools/aidl/aidl_language_y.yy  
[  0% 39/75651] lex out/soong/.intermediates/system/tools/aidl/libaidl-common/darwin_x86_64_static/gen/lex/system/tools/aidl/aidl_language_l.cpp
ninja: build stopped: subcommand failed.  
14:24:58 ninja failed with: exit status 1  

It means that bison isn't working. If you try running bison by running this command for example:

./prebuilts/misc/darwin-x86/bison/bison

it fails on error

Illegal instruction: 4  

The solution to this is to fix bison, since it's broken on High Sierra, by applying this patch from the folx at Mac Ports- https://raw.githubusercontent.com/macports/macports-ports/14451f57e89/devel/bison/files/secure_snprintf.patch

To apply this patch:
- Navigate to the bison source directory at:

cd external/bison  
  • Save it as a plain text file as name.patch in the bison directory by coping the text and using
pbpaste > patch-high-sierra.patch  

(or any other way you'd prefer to save it)

  • Apply the patch to the source code (p level depends on which dir you're currently in)
patch -p0 < patch-high-sierra.patch  
  • Navigate back on the root tree
cd ../..  
  • Make bison from source
make bison  
  • Copy bison from the bison directory from the out directory where AOSP is looking for it
cp ./out/host/darwin-x86/obj/EXECUTABLES/bison_intermediates/bison ./prebuilts/misc/darwin-x86/bison/bison  

And that'll fix it! Now you can run the AOSP normally.
🎉🎉🎉🎉🎉🎉🎉