Expose compiler-builtins-weak-intrinsics feature for -Zbuild-std

This was added in rust-lang/compiler-builtins#526 to force all
compiler-builtins intrinsics to use weak linkage.

Author: Amanieu

library/alloc/Cargo.toml

@@ -35,3 +35,4 @@ compiler-builtins-mem = ['compiler_builtins/mem']
 compiler-builtins-c = ["compiler_builtins/c"]
 compiler-builtins-no-asm = ["compiler_builtins/no-asm"]
 compiler-builtins-mangled-names = ["compiler_builtins/mangled-names"]
+compiler-builtins-weak-intrinsics = ["compiler_builtins/weak-intrinsics"]

library/std/Cargo.toml

@@ -65,6 +65,7 @@ compiler-builtins-c = ["alloc/compiler-builtins-c"]
 compiler-builtins-mem = ["alloc/compiler-builtins-mem"]
 compiler-builtins-no-asm = ["alloc/compiler-builtins-no-asm"]
 compiler-builtins-mangled-names = ["alloc/compiler-builtins-mangled-names"]
+compiler-builtins-weak-intrinsics = ["alloc/compiler-builtins-weak-intrinsics"]
 llvm-libunwind = ["unwind/llvm-libunwind"]
 system-llvm-libunwind = ["unwind/system-llvm-libunwind"]
 

library/sysroot/Cargo.toml

@@ -17,6 +17,7 @@ compiler-builtins-c = ["std/compiler-builtins-c"]
 compiler-builtins-mem = ["std/compiler-builtins-mem"]
 compiler-builtins-no-asm = ["std/compiler-builtins-no-asm"]
 compiler-builtins-mangled-names = ["std/compiler-builtins-mangled-names"]
+compiler-builtins-weak-intrinsics = ["std/compiler-builtins-weak-intrinsics"]
 llvm-libunwind = ["std/llvm-libunwind"]
 system-llvm-libunwind = ["std/system-llvm-libunwind"]
 panic-unwind = ["std/panic_unwind"]