Clean up linker architecture macros.

We don't need our own architecture macros; the standard ones will do.

This patch also fixes some __x86_64__ tests to be USE_RELA tests instead,
because they're not actually x86_64-specific.

I've cleaned up architecture-specific code slightly so where possible
all the code corresponding to a particular architecture is together.

This patch also fixes a bug in LP64 DT_PLTGOT handling, which should be
an error rather than falling through into DT_DEBUG! There was another #ifdef
bug where we'd only report unexpected DT_ entries on MIPS.

Change-Id: Id1d04e372611f641c1aa278a18e379f28af9eaf5

linker/linker_phdr.cpp

@@ -202,13 +202,13 @@ bool ElfReader::VerifyElfHeader() {
   }
 
   if (header_.e_machine !=
-#ifdef ANDROID_ARM_LINKER
+#if defined(__arm__)
       EM_ARM
-#elif defined(ANDROID_MIPS_LINKER)
-      EM_MIPS
-#elif defined(ANDROID_X86_LINKER)
+#elif defined(__i386__)
       EM_386
-#elif defined(ANDROID_X86_64_LINKER)
+#elif defined(__mips__)
+      EM_MIPS
+#elif defined(__x86_64__)
       EM_X86_64
 #endif
   ) {
@@ -321,10 +321,6 @@ bool ElfReader::ReserveAddressSpace() {
   return true;
 }
 
-// Map all loadable segments in process' address space.
-// This assumes you already called phdr_table_reserve_memory to
-// reserve the address space range for the library.
-// TODO: assert assumption.
 bool ElfReader::LoadSegments() {
   for (size_t i = 0; i < phdr_num_; ++i) {
     const Elf_Phdr* phdr = &phdr_table_[i];
@@ -513,7 +509,7 @@ int phdr_table_protect_gnu_relro(const Elf_Phdr* phdr_table, size_t phdr_count,
     return _phdr_table_set_gnu_relro_prot(phdr_table, phdr_count, load_bias, PROT_READ);
 }
 
-#ifdef ANDROID_ARM_LINKER
+#if defined(__arm__)
 
 #  ifndef PT_ARM_EXIDX
 #    define PT_ARM_EXIDX    0x70000001      /* .ARM.exidx segment */
@@ -550,7 +546,7 @@ int phdr_table_get_arm_exidx(const Elf_Phdr* phdr_table, size_t phdr_count,
     *arm_exidx_count = 0;
     return -1;
 }
-#endif /* ANDROID_ARM_LINKER */
+#endif
 
 /* Return the address and size of the ELF file's .dynamic section in memory,
  * or NULL if missing.