MLECO-3110: Fix for warnings from TensorFlow Lite Micro

Changes to fix "Pillow not found" warnings from TensorFlow
Lite Micro build.

Change-Id: I42a9b3f6df746ac3e34585e0c79ffdf35da97aef
Signed-off-by: Kshitij Sisodia <kshitij.sisodia@arm.com>
diff --git a/scripts/cmake/tensorflow.cmake b/scripts/cmake/tensorflow.cmake
index 127724b..2374c86 100644
--- a/scripts/cmake/tensorflow.cmake
+++ b/scripts/cmake/tensorflow.cmake
@@ -72,11 +72,18 @@
 list(APPEND MAKE_TARGETS_LIST "microlite")
 message(STATUS "TensorFlow Lite Micro build to be called for these targets: ${MAKE_TARGETS_LIST}")
 
+# Add virtual environment's Python directory path to the system path.
+# NOTE: This path is passed to the TensorFlow Lite Micro's make env
+# as it depends on some basic Python packages (like Pillow) installed
+# and the system-wide Python installation might not have them.
+set(ENV_PATH "${PYTHON_VENV}/bin:$ENV{PATH}")
+
 # Commands and targets
 add_custom_target(tensorflow_build ALL
 
     # Command to build the TensorFlow Lite Micro library
-    COMMAND make -j${J} -f ${TENSORFLOW_LITE_MICRO_PATH}/tools/make/Makefile ${MAKE_TARGETS_LIST}
+    COMMAND ${CMAKE_COMMAND} -E env PATH=${ENV_PATH}
+        make -j${J} -f ${TENSORFLOW_LITE_MICRO_PATH}/tools/make/Makefile ${MAKE_TARGETS_LIST}
         TARGET_TOOLCHAIN_ROOT=${TENSORFLOW_LITE_MICRO_TARGET_TOOLCHAIN_ROOT}
         TOOLCHAIN=${TENSORFLOW_LITE_MICRO_TOOLCHAIN}
         GENDIR=${TENSORFLOW_LITE_MICRO_GENDIR}
@@ -127,4 +134,4 @@
 
 target_compile_definitions(tensorflow-lite-micro
     INTERFACE
-    TF_LITE_STATIC_MEMORY)
\ No newline at end of file
+    TF_LITE_STATIC_MEMORY)