ltp: Declare #included .c files in extra_include_dir_deps

LTP float and realtime test sources directly #include
testcases/misc/math/float/main.c,
testcases/misc/math/float/thread_code.c, and
testcases/realtime/func/pi-tests/test-skeleton.c. Add them to
extra_include_dir_deps on ltp_test_defaults in Android.bp.

Bug: 532185687
Test: CI and m vts_ltp_test_x86_64
Flag: EXEMPT TEST_ONLY
Change-Id: I252ec0bab528b85d3794593056d41995eaa8674a