Rename jerry-libm to jerry-math (#4410)

That "libm" in the name of the library resulted in awkward naming
on *nix systems (`libjerry-libm.*`, "lib" occurring twice). And the
name of the corresponding header is `math.h` anyway.

Note that this is a breaking change in some sense. The commit
contains no API change, but the build system does change for users
of the math library.

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

targets/nuttx-stm32f4/README.md

@@ -41,7 +41,7 @@ jerryscript/tools/build.py \
     --clean \
     --lto=OFF \
     --jerry-cmdline=OFF \
-    --jerry-libm=ON \
+    --jerry-math=ON \
     --all-in-one=ON \
     --mem-heap=70 \
     --profile=es.next \