Add unit testing of fdlibm

The project is relying on a variant of fdlibm, which has aleady
been edited but never verified for correctness. This patch adds
unit testing of fdlibm by:

* introducing a test generator that uses a trusted libm
  implementation to calculate correct and expected results of math
  functions
  (tools/gen-test-fdlibm.sh and tools/unit-tests/gen-test-fdlibm.c),
* adding tests created with the generator that stress all publicly
  exported functions of jerry's fdlibm
  (tests/unit/test-fdlibm.inc.h), and
* adding a unit test file to drive the generated tests
  (tests/unit/test-fdlibm.c).

Note: The test generator is not expected to be executed often, thus
it is not wired into the build system. If it gets edited, it must
be used locally to re-generate the .inc.h file.

During development, it turned out that tests/unit/test-common.h
included the system header math.h, which was only a bad smell until
now but became a real header conflict issue with the introduction
of the fdlibm unit test. Thus, this patch also changes the include
to fdlibm-math.h.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

tests/unit/test-common.h

@@ -18,7 +18,7 @@
 
 #include "jrt.h"
 
-#include <math.h>
+#include "fdlibm-math.h"
 #include <setjmp.h>
 #include <stdio.h>
 #include <stdlib.h>