Rollup merge of rust-lang#60685 - dtolnay:spdx, r=nikomatsakis

Switch to SPDX 2.1 license expression

[According to the Cargo Reference:](https://doc.rust-lang.org/cargo/reference/manifest.html)

> This is an SPDX 2.1 license expression for this package. Currently crates.io will validate the license provided against a whitelist of known license and exception identifiers from the SPDX license list 2.4. Parentheses are not currently supported.
>
> Multiple licenses can be separated with a \`/\`, although that usage is deprecated. Instead, use a license expression with AND and OR operators to get more explicit semantics.

The notation with slashes is deprecated in favor of explicit AND or OR.

As I understand it, Rust's license is MIT *OR* Apache-2.0 matching the meaning of *OR* defined by [SPDX Specification 2.1](https://spdx.org/spdx-specification-21-web-version):

> If presented with a choice between two or more licenses, use the disjunctive binary "OR" operator to construct a new license expression, where both the left and right operands are valid license expression values.

Author: Centril

src/libstd/Cargo.toml

@@ -3,7 +3,7 @@ authors = ["The Rust Project Developers"]
 name = "std"
 version = "0.0.0"
 build = "build.rs"
-license = "MIT/Apache-2.0"
+license = "MIT OR Apache-2.0"
 repository = "https://github.com/rust-lang/rust.git"
 description = "The Rust Standard Library"
 edition = "2018"

src/tools/rustbook/Cargo.toml

@@ -2,7 +2,7 @@
 authors = ["The Rust Project Developers"]
 name = "rustbook"
 version = "0.1.0"
-license = "MIT/Apache-2.0"
+license = "MIT OR Apache-2.0"
 edition = "2018"
 
 [dependencies]

src/tools/rustc-std-workspace-alloc/Cargo.toml

@@ -2,7 +2,7 @@
 name = "rustc-std-workspace-alloc"
 version = "1.0.0"
 authors = ["Alex Crichton <[email protected]>"]
-license = 'MIT/Apache-2.0'
+license = 'MIT OR Apache-2.0'
 description = """
 Hack for the compiler's own build system
 """

src/tools/rustc-std-workspace-core/Cargo.toml

@@ -2,7 +2,7 @@
 name = "rustc-std-workspace-core"
 version = "1.0.0"
 authors = ["Alex Crichton <[email protected]>"]
-license = 'MIT/Apache-2.0'
+license = 'MIT OR Apache-2.0'
 description = """
 Hack for the compiler's own build system
 """

src/tools/rustc-workspace-hack/Cargo.toml

@@ -2,7 +2,7 @@
 name = "rustc-workspace-hack"
 version = "1.0.0"
 authors = ["Alex Crichton <[email protected]>"]
-license = 'MIT/Apache-2.0'
+license = 'MIT OR Apache-2.0'
 description = """
 Hack for the compiler's own build system
 """

src/tools/unstable-book-gen/Cargo.toml

@@ -3,7 +3,7 @@ authors = ["est31 <[email protected]>",
            "The Rust Project Developers"]
 name = "unstable-book-gen"
 version = "0.1.0"
-license = "MIT/Apache-2.0"
+license = "MIT OR Apache-2.0"
 edition = "2018"
 
 [dependencies]