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

jerry-math/libjerry-math.pc.in

@@ -0,0 +1,10 @@
+prefix=@CMAKE_INSTALL_PREFIX@
+libdir=${prefix}/lib
+includedir=${prefix}/include/jerry-math
+
+Name: libjerry-math
+Description: JerryScript: lightweight JavaScript engine (minimal math library)
+URL: https://github.com/jerryscript-project/jerryscript
+Version: @JERRY_VERSION@
+Libs: -L${libdir} -ljerry-math
+Cflags: -I${includedir}