Rollup merge of rust-lang#78947 - dalance:llvm_cov, r=Mark-Simulacrum

Ship llvm-cov through llvm-tools

`llvm-cov` is used to generate coverage report with LLVM InstrProf-based code coverage rust-lang#34701.
So if `llvm-cov` is shipped through llvm-tools, users can try it easily accorging to the instruction of [The Rust Unstable Book](https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/source-based-code-coverage.html).

src/bootstrap/lib.rs

@@ -169,17 +169,18 @@ pub use crate::config::Config;
 pub use crate::flags::Subcommand;
 
 const LLVM_TOOLS: &[&str] = &[
-    "llvm-nm", // used to inspect binaries; it shows symbol names, their sizes and visibility
-    "llvm-objcopy", // used to transform ELFs into binary format which flashing tools consume
-    "llvm-objdump", // used to disassemble programs
+    "llvm-cov",      // used to generate coverage report
+    "llvm-nm",       // used to inspect binaries; it shows symbol names, their sizes and visibility
+    "llvm-objcopy",  // used to transform ELFs into binary format which flashing tools consume
+    "llvm-objdump",  // used to disassemble programs
     "llvm-profdata", // used to inspect and merge files generated by profiles
-    "llvm-readobj", // used to get information from ELFs/objects that the other tools don't provide
-    "llvm-size", // used to prints the size of the linker sections of a program
-    "llvm-strip", // used to discard symbols from binary files to reduce their size
-    "llvm-ar", // used for creating and modifying archive files
-    "llvm-dis", // used to disassemble LLVM bitcode
-    "llc",     // used to compile LLVM bytecode
-    "opt",     // used to optimize LLVM bytecode
+    "llvm-readobj",  // used to get information from ELFs/objects that the other tools don't provide
+    "llvm-size",     // used to prints the size of the linker sections of a program
+    "llvm-strip",    // used to discard symbols from binary files to reduce their size
+    "llvm-ar",       // used for creating and modifying archive files
+    "llvm-dis",      // used to disassemble LLVM bitcode
+    "llc",           // used to compile LLVM bytecode
+    "opt",           // used to optimize LLVM bytecode
 ];
 
 pub const VERSION: usize = 2;