[efi] Use POSIX version of basename() in elf2efi.c

This is required in order to build on Mac OS X.

Suggested-by: Joshua Oreman <oremanj@rwcr.net>

src/util/elf2efi.c

 #include <bfd.h>
 #include <gpxe/efi/efi.h>
 #include <gpxe/efi/IndustryStandard/PeImage.h>
+#include <libgen.h>
 
 #define eprintf(...) fprintf ( stderr, __VA_ARGS__ )
 
  */
 static void elf2pe ( const char *elf_name, const char *pe_name,
 		     struct options *opts ) {
+	char pe_name_tmp[ strlen ( pe_name ) + 1 ];
 	bfd *bfd;
 	asymbol **symtab;
 	asection *section;
 	struct pe_header pe_header;
 	FILE *pe;
 
+	/* Create a modifiable copy of the PE name */
+	memcpy ( pe_name_tmp, pe_name, sizeof ( pe_name_tmp ) );
+
 	/* Open the file */
 	bfd = open_input_bfd ( elf_name );
 	symtab = read_symtab ( bfd );
 
 	/* Create the .reloc section */
 	*(next_pe_section) = create_debug_section ( &pe_header,
-						    basename ( pe_name ) );
+						    basename ( pe_name_tmp ) );
 	next_pe_section = &(*next_pe_section)->next;
 
 	/* Write out PE file */