Initial support for building RISC-V runtimes targeting PolkaVM (#3179)

This PR adds initial support for building RISC-V runtimes targeting
PolkaVM.

- Setting the `SUBSTRATE_RUNTIME_TARGET=riscv` environment variable will
now build a RISC-V runtime instead of a WASM runtime.
- This only adds support for *building* runtimes; running them will need
a PolkaVM-based executor, which I will add in a future PR.
- Only building the minimal runtime is supported (building the Polkadot
runtime doesn't work *yet* due to one of the dependencies).
- The builder now sets a `substrate_runtime` cfg flag when building the
runtimes, with the idea being that instead of doing `#[cfg(not(feature =
"std"))]` or `#[cfg(target_arch = "wasm32")]` to detect that we're
building a runtime you'll do `#[cfg(substrate_runtime)]`. (Switching the
whole codebase to use this will be done in a future PR; I deliberately
didn't do this here to keep this PR minimal and reviewable.)
- Further renaming of things (e.g. types, environment variables and proc
macro attributes having "wasm" in their name) to be target-agnostic will
also be done in a future refactoring PR (while keeping backwards
compatibility where it makes sense; I don't intend to break anyone's
workflow or create unnecessary churn).
- This PR also fixes two bugs in the `wasm-builder` crate:
* The `RUSTC` environment variable is now removed when invoking the
compiler. This prevents the toolchain version from being overridden when
called from a `build.rs` script.
* When parsing the `rustup toolchain list` output the `(default)` is now
properly stripped and not treated as part of the version.
- I've also added a minimal CI job that makes sure this doesn't break in
the future. (cc @paritytech/ci)

cc @athei

------

Also, just a fun little tidbit: quickly comparing the size of the built
runtimes it seems that the PolkaVM runtime is slightly smaller than the
WASM one. (`production` build, with the `names` section substracted from
the WASM's size to keep things fair, since for the PolkaVM runtime we're
currently stripping out everything)

- `.wasm`: 625505 bytes
- `.wasm` (after wasm-opt -O3): 563205 bytes
- `.wasm` (after wasm-opt -Os): 562987 bytes
- `.wasm` (after wasm-opt -Oz): 536852 bytes
- `.polkavm`: ~~580338 bytes~~ 550476 bytes (after enabling extra target
features; I'll add those in another PR once we have an executor working)

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

Cargo.lock

@@ -9571,7 +9571,7 @@ dependencies = [
  "anyhow",
  "frame-system",
  "parity-wasm",
- "polkavm-linker",
+ "polkavm-linker 0.5.0",
  "sp-runtime",
  "tempfile",
  "toml 0.8.8",
@@ -9633,7 +9633,7 @@ dependencies = [
  "bitflags 1.3.2",
  "parity-scale-codec",
  "paste",
- "polkavm-derive",
+ "polkavm-derive 0.5.0",
  "scale-info",
 ]
 
@@ -13711,28 +13711,65 @@ version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "88b4e215c80fe876147f3d58158d5dfeae7dabdd6047e175af77095b78d0035c"
 
+[[package]]
+name = "polkavm-common"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "92c99f7eee94e7be43ba37eef65ad0ee8cbaf89b7c00001c3f6d2be985cb1817"
+
 [[package]]
 name = "polkavm-derive"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6380dbe1fb03ecc74ad55d841cfc75480222d153ba69ddcb00977866cbdabdb8"
 dependencies = [
- "polkavm-derive-impl",
+ "polkavm-derive-impl 0.5.0",
  "syn 2.0.48",
 ]
 
+[[package]]
+name = "polkavm-derive"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "79fa916f7962348bd1bb1a65a83401675e6fc86c51a0fdbcf92a3108e58e6125"
+dependencies = [
+ "polkavm-derive-impl-macro",
+]
+
 [[package]]
 name = "polkavm-derive-impl"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dc8211b3365bbafb2fb32057d68b0e1ca55d079f5cf6f9da9b98079b94b3987d"
 dependencies = [
- "polkavm-common",
+ "polkavm-common 0.5.0",
  "proc-macro2",
  "quote",
  "syn 2.0.48",
 ]
 
+[[package]]
+name = "polkavm-derive-impl"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c10b2654a8a10a83c260bfb93e97b262cf0017494ab94a65d389e0eda6de6c9c"
+dependencies = [
+ "polkavm-common 0.8.0",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.48",
+]
+
+[[package]]
+name = "polkavm-derive-impl-macro"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "15e85319a0d5129dc9f021c62607e0804f5fb777a05cdda44d750ac0732def66"
+dependencies = [
+ "polkavm-derive-impl 0.8.0",
+ "syn 2.0.48",
+]
+
 [[package]]
 name = "polkavm-linker"
 version = "0.5.0"
@@ -13743,7 +13780,22 @@ dependencies = [
  "hashbrown 0.14.3",
  "log",
  "object 0.32.2",
- "polkavm-common",
+ "polkavm-common 0.5.0",
+ "regalloc2 0.9.3",
+ "rustc-demangle",
+]
+
+[[package]]
+name = "polkavm-linker"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1bc03593918a5890f96c276fb1e34ab77002bea1f9136cdcb55107c241011ab7"
+dependencies = [
+ "gimli 0.28.0",
+ "hashbrown 0.14.3",
+ "log",
+ "object 0.32.2",
+ "polkavm-common 0.8.0",
  "regalloc2 0.9.3",
  "rustc-demangle",
 ]
@@ -17945,6 +17997,7 @@ dependencies = [
  "sp-externalities 0.25.0",
  "sp-metadata-ir",
  "sp-runtime",
+ "sp-runtime-interface 24.0.0",
  "sp-state-machine",
  "sp-std 14.0.0",
  "sp-test-primitives",
@@ -18632,6 +18685,7 @@ dependencies = [
  "bytes",
  "impl-trait-for-tuples",
  "parity-scale-codec",
+ "polkavm-derive 0.8.0",
  "primitive-types",
  "rustversion",
  "sp-core",
@@ -19647,6 +19701,7 @@ dependencies = [
  "console",
  "filetime",
  "parity-wasm",
+ "polkavm-linker 0.8.1",
  "sp-maybe-compressed-blob",
  "strum 0.24.1",
  "tempfile",