Android: Fixes for Q and R

Fix Android-Q build:
- Use AOSP prebuilt bison by specifying $(BISON) variable
- Use AOSP prebuilt flex by specifying $(LEX) variable

Fix Android-R build:
- Add M4 environmet variable for Android R and higher (See [1])

[1] - https://cs.android.com/android/_/android/platform/build/+/2bfffb9f48a78de12faf5da77424c0cecb70d6eb:Changes.md;dlc=997661002af1282d938e88c3c723037e42e5d283

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Tested-by: Mauro Rossi <issor.oruam@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5894>
diff --git a/Android.mk b/Android.mk
index c15c2b7..6181bbe8 100644
--- a/Android.mk
+++ b/Android.mk
@@ -44,6 +44,11 @@
 MESA_COMMON_MK := $(MESA_TOP)/Android.common.mk
 MESA_PYTHON2 := python
 MESA_PYTHON3 := python3
+ifeq ($(filter 5 6 7 8 9 10, $(MESA_ANDROID_MAJOR_VERSION)),)
+MESA_LEX     := M4=$(M4) $(LEX)
+else
+MESA_LEX     := $(LEX)
+endif
 
 # Lists to convert driver names to boolean variables
 # in form of <driver name>.<boolean make variable>