Add missing "-mlongcalls" flag to PlatformIO build script (espressif#4420)

Fixes possible issues with assembly files in external libraries

Author: valeros

tools/platformio-build.py

@@ -35,7 +35,7 @@
 assert isdir(FRAMEWORK_DIR)
 
 env.Append(
-    ASFLAGS=["-x", "assembler-with-cpp"],
+    ASFLAGS=["-x", "assembler-with-cpp", "-mlongcalls"],
 
     CFLAGS=[
         "-std=gnu99",