build: add "fastest-runtime" profile for runtime optimization (#8554)

This is extremely useful for cases where the default optimizations just
are not enough.

Background: [neovim](https://github.com/neovim/neovim) is interested to
add wasmtime support in https://github.com/neovim/neovim/pull/28415 but
we noticed that including wasmtime, even when not using wasmtime
directly, heavily affects runtime performance. This is not only
reflected in the increased startuptime but affects the runtime
performance overall.

Here are the benchmarks for startuptimes for different configurations.
Important to note is that all of runtime is affected, but the
startuptime is a decent proxy to measure runtime performance:

```
No wasm
  Time (mean ± σ):      50.5 ms ±   1.5 ms    [User: 32.8 ms, System: 12.3 ms]
  Range (min … max):    48.3 ms …  54.4 ms    56 runs

Wasm, lto=thin
  Time (mean ± σ):     104.9 ms ±   3.5 ms    [User: 86.5 ms, System: 12.7 ms]
  Range (min … max):    99.5 ms … 111.1 ms    26 runs

Wasm, lto=true
  Time (mean ± σ):      83.8 ms ±   2.5 ms    [User: 65.8 ms, System: 12.1 ms]
  Range (min … max):    80.5 ms …  93.3 ms    31 runs

Wasm, lto=true, strip="none", incremental=false, codegen-units=1, panic="abort"
  Time (mean ± σ):      53.1 ms ±   1.0 ms    [User: 35.5 ms, System: 12.5 ms]
  Range (min … max):    50.6 ms …  55.5 ms    54 runs
```

Cargo.toml

@@ -457,3 +457,8 @@ incremental = false
 debug-assertions = false
 overflow-checks = false
 opt-level = 's'
+
+[profile.fastest-runtime]
+inherits = "release"
+codegen-units = 1
+lto = true

crates/c-api/CMakeLists.txt

@@ -4,15 +4,23 @@ project(wasmtime C)
 set(WASMTIME_USER_CARGO_BUILD_OPTIONS "" CACHE STRING "Additional cargo flags (such as --features) to apply to the build command")
 option(BUILD_SHARED_LIBS "Build using shared libraries" OFF)
 option(WASMTIME_ALWAYS_BUILD "If cmake should always invoke cargo to build wasmtime" ON)
+option(WASMTIME_FASTEST_RUNTIME "Set flags designed to optimize runtime performance" OFF)
 
-if(CMAKE_BUILD_TYPE STREQUAL "Release" OR
-	CMAKE_BUILD_TYPE STREQUAL "MinSizeRel" OR
-	CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo"
-)
-	set(WASMTIME_BUILD_TYPE_FLAG "--release")
-	set(WASMTIME_BUILD_TYPE "release")
+if(WASMTIME_FASTEST_RUNTIME)
+	set(WASMTIME_BUILD_TYPE_FLAG "--profile=fastest-runtime")
+	set(WASMTIME_BUILD_TYPE "fastest-runtime")
+	set(CARGO_PROFILE_PANIC CARGO_PROFILE_RELEASE_PANIC)
 else()
-	set(WASMTIME_BUILD_TYPE "debug")
+	if(CMAKE_BUILD_TYPE STREQUAL "Release" OR
+	    CMAKE_BUILD_TYPE STREQUAL "MinSizeRel" OR
+	    CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo")
+		set(WASMTIME_BUILD_TYPE_FLAG "--release")
+		set(WASMTIME_BUILD_TYPE "release")
+		set(CARGO_PROFILE_PANIC CARGO_PROFILE_RELEASE_PANIC)
+	else()
+		set(WASMTIME_BUILD_TYPE "debug")
+		set(CARGO_PROFILE_PANIC CARGO_PROFILE_DEBUG_PANIC)
+    endif()
 endif()
 
 if(ANDROID)
@@ -89,7 +97,9 @@ ExternalProject_Add(
 	DOWNLOAD_COMMAND ""
 	CONFIGURE_COMMAND ""
 	INSTALL_COMMAND "${WASMTIME_INSTALL_COMMAND}"
-        BUILD_COMMAND ${WASMTIME_PREBUILD_COMMAND} ${WASMTIME_CARGO_BINARY} build ${WASMTIME_BUILD_TYPE_FLAG} ${WASMTIME_USER_CARGO_BUILD_OPTIONS} ${WASMTIME_BUILD_TARGET}
+        BUILD_COMMAND
+            ${CMAKE_COMMAND} -E env ${CARGO_PROFILE_PANIC}=abort
+            ${WASMTIME_PREBUILD_COMMAND} ${WASMTIME_CARGO_BINARY} build ${WASMTIME_BUILD_TYPE_FLAG} ${WASMTIME_USER_CARGO_BUILD_OPTIONS} ${WASMTIME_BUILD_TARGET}
 	USES_TERMINAL_BUILD TRUE
 	BINARY_DIR ${CMAKE_CURRENT_SOURCE_DIR}/artifact
         BUILD_ALWAYS ${WASMTIME_ALWAYS_BUILD}