Point CMake to the correct Ninja

Change-Id: I5879b7985d313f1787f293ae199df90e946550c9
diff --git a/scripts/build.sh b/scripts/build.sh
index 5d73aa0..0e03a8b 100755
--- a/scripts/build.sh
+++ b/scripts/build.sh
@@ -20,7 +20,8 @@
 BORINGSSL_BUILD="${BORINGSSL_SRC}/build"
 mkdir -p -- "${BORINGSSL_BUILD}"
 pushd "${BORINGSSL_BUILD}"
-[[ -f "${BORINGSSL_BUILD}/build.ninja" ]] || cmake -GNinja \
+[[ -f "${BORINGSSL_BUILD}/build.ninja" ]] || ${CMAKE_PROGRAM} -GNinja \
+  -DCMAKE_MAKE_PROGRAM=${NINJA_PROGRAM} \
   -DCMAKE_BUILD_TYPE=Release \
   -DCMAKE_C_FLAGS=-fPIC \
   ..
@@ -32,6 +33,7 @@
 mkdir -p -- "${LIBSSH2_BUILD}"
 pushd "${LIBSSH2_BUILD}"
 [[ -f "${LIBSSH2_BUILD}/build.ninja" ]] || ${CMAKE_PROGRAM} -GNinja \
+  -DCMAKE_MAKE_PROGRAM=${NINJA_PROGRAM} \
   -DCMAKE_BUILD_TYPE=Release \
   -DBUILD_SHARED_LIBS=OFF \
   -DENABLE_ZLIB_COMPRESSION=ON \
@@ -50,6 +52,7 @@
 mkdir -p -- "${CURL_BUILD}"
 pushd "${CURL_BUILD}"
 [[ -f "${CURL_BUILD}/build.ninja" ]] || ${CMAKE_PROGRAM} -GNinja \
+  -DCMAKE_MAKE_PROGRAM=${NINJA_PROGRAM} \
   -DCMAKE_BUILD_TYPE=Release \
   -DBUILD_CURL_EXE=OFF \
   -DBUILD_TESTING=OFF \
@@ -71,6 +74,7 @@
 mkdir -p "${LIBGIT2_BUILD}"
 pushd "${LIBGIT2_BUILD}"
 [[ -f "${LIBGIT2_BUILD}/build.ninja" ]] || ${CMAKE_PROGRAM} -GNinja \
+  -DCMAKE_MAKE_PROGRAM=${NINJA_PROGRAM} \
   -DCMAKE_BUILD_TYPE=Release \
   -DCMAKE_C_FLAGS=-fPIC \
   -DTHREADSAFE=ON \