Add dynamic linkers in alternative libdirs for x86/amd64/ppc
such that all variants found in gentoo profiles are covered.

--- prelink-cross-20151030/src/arch-i386.c
+++ prelink-cross-20151030/src/arch-i386.c
@@ -1099,6 +1099,7 @@ PL_ARCH(i386) = {
   .R_RELATIVE = R_386_RELATIVE,
   .rtype_class_valid = RTYPE_CLASS_VALID,
   .dynamic_linker = "/lib/ld-linux.so.2",
+  .dynamic_linker_alt = "/lib32/ld-linux.so.2",
   .adjust_dyn = i386_adjust_dyn,
   .adjust_rel = i386_adjust_rel,
   .adjust_rela = i386_adjust_rela,
--- prelink-cross-20151030/src/arch-x86_64.c
+++ prelink-cross-20151030/src/arch-x86_64.c
@@ -574,6 +574,7 @@ PL_ARCH(x32) = {
   .R_RELATIVE = R_X86_64_RELATIVE,
   .rtype_class_valid = RTYPE_CLASS_VALID,
   .dynamic_linker = "/libx32/ld-linux-x32.so.2",
+  .dynamic_linker_alt = "/lib/ld-linux-x32.so.2",
   .adjust_dyn = x86_64_adjust_dyn,
   .adjust_rel = x86_64_adjust_rel,
   .adjust_rela = x86_64_adjust_rela,
@@ -613,6 +614,7 @@ PL_ARCH(x86_64) = {
   .R_RELATIVE = R_X86_64_RELATIVE,
   .rtype_class_valid = RTYPE_CLASS_VALID,
   .dynamic_linker = "/lib64/ld-linux-x86-64.so.2",
+  .dynamic_linker_alt = "/lib/ld-linux-x86-64.so.2",
   .adjust_dyn = x86_64_adjust_dyn,
   .adjust_rel = x86_64_adjust_rel,
   .adjust_rela = x86_64_adjust_rela,
--- prelink-cross-20151030/src/arch-ppc.c
+++ prelink-cross-20151030/src/arch-ppc.c
@@ -1160,6 +1160,7 @@ PL_ARCH(ppc) = {
   .R_RELATIVE = R_PPC_RELATIVE,
   .rtype_class_valid = RTYPE_CLASS_VALID,
   .dynamic_linker = "/lib/ld.so.1",
+  .dynamic_linker_alt = "/lib32/ld.so.1",
   .adjust_dyn = ppc_adjust_dyn,
   .adjust_rel = ppc_adjust_rel,
   .adjust_rela = ppc_adjust_rela,
--- prelink-cross-20151030/src/arch-ppc64.c
+++ prelink-cross-20151030/src/arch-ppc64.c
@@ -869,6 +869,7 @@ PL_ARCH(ppc64) = {
   .R_RELATIVE = R_PPC64_RELATIVE,
   .rtype_class_valid = RTYPE_CLASS_PLT,
   .dynamic_linker = "/lib64/ld64.so.1",
+  .dynamic_linker_alt = "/lib/ld64.so.1",
   .adjust_section = ppc64_adjust_section,
   .adjust_dyn = ppc64_adjust_dyn,
   .adjust_rel = ppc64_adjust_rel,