Rename filenames prone to include path conflicts

E.g. when used uninstalled as a submodule.

configure

@@ -492,7 +492,7 @@ for v in $confvars ; do
   fi
 done
 
-version=`head $source_path/VERSION`
+version=`head $source_path/VERSION.txt`
 echo "VERSION = $version" >> config.mak
 echo "#define TCC_VERSION \"$version\"" >> $TMPH
 echo "@set VERSION $version" > config.texi

tcc.h

@@ -319,7 +319,7 @@ extern long double strtold (const char *__nptr, char **__endptr);
 /* -------------------------------------------- */
 
 #include "libtcc.h"
-#include "elf.h"
+#include "tccelf.h"
 #include "stab.h"
 
 /* -------------------------------------------- */