proot: Properly handle relocated embedded loader

The _binary_loader_exe_size variable can be relocated by Android linker
which makes it unusable, rely instead on end-start which can be
relocated

Also don't reject binaries with linker having it's own DT_INTERP section
(like /system/bin/linker on ARM Android)

disabled-packages/proot/src-execve-enter.c.patch

@@ -0,0 +1,42 @@
+--- PRoot-5.1.0/src/execve/enter.c	2014-12-15 15:18:11.000000000 +0100
++++ src/src/execve/enter.c	2016-03-20 12:05:08.013426156 +0100
+@@ -454,10 +454,10 @@
+ }
+ 
+ extern unsigned char _binary_loader_exe_start;
+-extern unsigned char _binary_loader_exe_size;
++extern unsigned char _binary_loader_exe_end;
+ 
+ extern unsigned char WEAK _binary_loader_m32_exe_start;
+-extern unsigned char WEAK _binary_loader_m32_exe_size;
++extern unsigned char WEAK _binary_loader_m32_exe_end;
+ 
+ /**
+  * Extract the built-in loader.  This function returns NULL if an
+@@ -483,11 +483,11 @@
+ 
+ 	if (wants_32bit_version) {
+ 		start = (void *) &_binary_loader_m32_exe_start;
+-		size  = (size_t) &_binary_loader_m32_exe_size;
++		size  = (size_t) (&_binary_loader_m32_exe_end - &_binary_loader_m32_exe_start);
+ 	}
+ 	else {
+ 		start = (void *) &_binary_loader_exe_start;
+-		size  = (size_t) &_binary_loader_exe_size;
++		size  = (size_t) (&_binary_loader_exe_end - &_binary_loader_exe_start);
+ 	}
+ 
+ 	status2 = write(fd, start, size);
+@@ -645,8 +645,10 @@
+ 
+ 		/* An ELF interpreter is supposed to be
+ 		 * standalone.  */
+-		if (tracee->load_info->interp->interp != NULL)
+-			return -EINVAL;
++		if (tracee->load_info->interp->interp != NULL) {
++			TALLOC_FREE(tracee->load_info->interp->interp);
++			// TODO: Print warning?
++		}
+ 	}
+ 
+ 	compute_load_addresses(tracee);