amd64-linux: DF_1_PIE marks a main program; stub juggles AT_PHDR for same

https://github.com/upx/upx/issues/105
	modified:   p_elf_enum.h
	modified:   p_lx_elf.cpp
	modified:   stub/src/amd64-linux.elf-main.c

	modified:   ../.github/travis_testsuite_1.sh
	modified:   stub/amd64-linux.elf-fold.h
	modified:   stub/tmp/amd64-linux.elf-fold.map

src/p_elf_enum.h

@@ -162,9 +162,14 @@
         DT_CHECKSUM = 0x6ffffdf8,       /* Only for prelink? */
         DT_GNU_HASH = 0x6ffffef5,       /* GNU-style hash table */
         DT_VERSYM   = 0x6ffffff0,       /* version[] for each symbol */
+        DT_FLAGS_1  = 0x6ffffffb,       /* DF_1_* */
         DT_VERDEF   = 0x6ffffffc,       /* version definitions[] */
         DT_VERNEEDED= 0x6ffffffe        /* version[] needed */
     };
+    enum { // DT_FLAGS_1
+        DF_1_NOW    = 0x00000001,  /* Set RTLD_NOW for this object.  */
+        DF_1_PIE    = 0x08000000   // Position-Independent Executable (main program)
+    };
 #endif