Make rlib metadata strip works with MIPSr6 architecture

Because MIPSr6 has many differences with previous MIPSr2 arch, the previous rlib metadata stripping code in `rustc_codegen_ssa` is only for MIPSr2/r3/r5 (which share the same elf e_flags).
This commit fixed this problem. It makes `rustc_codegen_ssa` happy when compiling rustc for MIPSr6 target or hosts.

Author: Fearyncess

compiler/rustc_codegen_ssa/Cargo.toml

@@ -41,6 +41,6 @@ rustc_target = { path = "../rustc_target" }
 rustc_session = { path = "../rustc_session" }
 
 [dependencies.object]
-version = "0.26.2"
+version = "0.27.0"
 default-features = false
 features = ["read_core", "elf", "macho", "pe", "unaligned", "archive", "write"]

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -135,12 +135,24 @@ fn create_object_file(sess: &Session) -> Option<write::Object> {
         Architecture::Mips => {
             // copied from `mipsel-linux-gnu-gcc foo.c -c` and
             // inspecting the resulting `e_flags` field.
-            let e_flags = elf::EF_MIPS_ARCH_32R2 | elf::EF_MIPS_CPIC | elf::EF_MIPS_PIC;
+            let e_flags = elf::EF_MIPS_CPIC
+                | elf::EF_MIPS_PIC
+                | if sess.target.options.cpu.contains("r6") {
+                    elf::EF_MIPS_ARCH_32R6 | elf::EF_MIPS_NAN2008
+                } else {
+                    elf::EF_MIPS_ARCH_32R2
+                };
             file.flags = FileFlags::Elf { e_flags };
         }
         Architecture::Mips64 => {
             // copied from `mips64el-linux-gnuabi64-gcc foo.c -c`
-            let e_flags = elf::EF_MIPS_ARCH_64R2 | elf::EF_MIPS_CPIC | elf::EF_MIPS_PIC;
+            let e_flags = elf::EF_MIPS_CPIC
+                | elf::EF_MIPS_PIC
+                | if sess.target.options.cpu.contains("r6") {
+                    elf::EF_MIPS_ARCH_64R6 | elf::EF_MIPS_NAN2008
+                } else {
+                    elf::EF_MIPS_ARCH_64R2
+                };
             file.flags = FileFlags::Elf { e_flags };
         }
         Architecture::Riscv64 if sess.target.options.features.contains("+d") => {