xerces-c: Use libstdcpp instead of uclibc++

Both dependent packages (sumo and libelektra) use (and must use) libstdcpp

Two libc++ cannot be linked against each other at the same time. I believe
this causes xerces-c to not be used even though it is listed as a
dependency.

Took the time to clean up the Makefile. Also replaced -fPIC with -fpic to
eliminate potential issues. Added linker flags for smaller size.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/libxerces-c/patches/0001-fix-configure-cross-compiling.patch

@@ -1,6 +1,6 @@
 --- a/configure.ac
 +++ b/configure.ac
-@@ -194,7 +194,7 @@ AC_COMPILE_IFELSE(  [AC_LANG_PROGRAM([[#
+@@ -228,7 +228,7 @@ AC_COMPILE_IFELSE(  [AC_LANG_PROGRAM([[#
                      ]
                   )
  AC_MSG_CHECKING([for wcsrtombs])
@@ -9,7 +9,7 @@
  #include <string.h>]],
                                   [[
  mbstate_t st;
-@@ -216,7 +216,7 @@ else
+@@ -250,7 +250,7 @@ else
                      ]
                   )
  AC_MSG_CHECKING([for mbsrtowcs])