LibC: Add stub for fnmatch and a set of defined values

This adds a stub for fnmatch and the following defined values:
- FNM_PATHNAME
- FNM_NOESCAPE
- FNM_PERIOD
- FNM_FILE_NAME
- FNM_LEADING_DIR
- FNM_CASEFOLD
- FNM_EXTMATCH

Userland/Libraries/LibC/CMakeLists.txt

@@ -7,6 +7,7 @@ set(LIBC_SOURCES
     dlfcn.cpp
     fcntl.cpp
     fenv.cpp
+    fnmatch.cpp
     getopt.cpp
     grp.cpp
     inttypes.cpp