Let runtime_loader ignore RT_RELRO program headers.

* The new libstdc++.so contains program headers of type PT_RELRO (for
  making segments read-only after relocation). While the actual feature
  has not been implemented, the runtime_loader should now silently
  accept (and ignore) those program headers.

headers/private/system/elf_common.h

@@ -141,6 +141,7 @@
 #define PT_PHDR		6
 #define PT_TLS		7
 #define PT_STACK	0x6474e551
+#define PT_RELRO	0x6474e552
 
 #define PT_LOPROC	0x70000000
 #define PT_HIPROC	0x7fffffff

src/system/runtime_loader/elf_load_image.cpp

@@ -75,6 +75,9 @@ count_regions(const char* imagePath, char const* buff, int phnum, int phentsize)
 			case PT_PHDR:
 				// we don't use it
 				break;
+			case PT_RELRO:
+				// not implemented yet, but can be ignored
+				break;
 			case PT_STACK:
 				// we don't use it
 				break;
@@ -196,6 +199,9 @@ parse_program_headers(image_t* image, char* buff, int phnum, int phentsize)
 			case PT_PHDR:
 				// we don't use it
 				break;
+			case PT_RELRO:
+				// not implemented yet, but can be ignored
+				break;
 			case PT_STACK:
 				// we don't use it
 				break;