build: disable zlib

This isn't needed, and causes issues when clang-tblgen
is built, but trys to reach for a system libz.so.

diff --git a/build.sh b/build.sh
index e25d2f732..ec8422621 100755
--- a/build.sh
+++ b/build.sh
@@ -66,6 +66,7 @@ cmake ../src/llvm \
  -DCMAKE_INSTALL_PREFIX=$INSTALLPREFIX \
  -DTAPI_REPOSITORY_STRING=$TAPI_VERSION \
  -DTAPI_FULL_VERSION=$TAPI_VERSION \
+ -DLLVM_ENABLE_ZLIB=OFF \
  $CMAKE_EXTRA_ARGS
 
 echo ""