build: add wasm targets for keeper (#33124)

[powdr](github.com/powdr-labs/powdr) has tested keeper in their womir
system and managed to get it to work. This PR adds wasm as a keeper
target. There's another plan by the zkevm team to support wasm with wasi
as well, so these PR adds both targets.

These currently uses the `example` tag, as there is no precompile
intefrace defined for either target yet. Nonetheless, this is useful for
testing these zkvms so it makes sense to support these experimental
targets already.

build/ci.go

@@ -107,6 +107,18 @@ var (
 			Tags: "ziren",
 			Env:  map[string]string{"GOMIPS": "softfloat", "CGO_ENABLED": "0"},
 		},
+		{
+			Name:   "wasm-js",
+			GOOS:   "js",
+			GOARCH: "wasm",
+			Tags:   "example",
+		},
+		{
+			Name:   "wasm-wasi",
+			GOOS:   "wasip1",
+			GOARCH: "wasm",
+			Tags:   "example",
+		},
 		{
 			Name: "example",
 			Tags: "example",
@@ -331,6 +343,10 @@ func buildFlags(env build.Environment, staticLinking bool, buildTags []string) (
 		}
 		ld = append(ld, "-extldflags", "'"+strings.Join(extld, " ")+"'")
 	}
+    // TODO(gballet): revisit after the input api has been defined
+	if runtime.GOARCH == "wasm" {
+		ld = append(ld, "-gcflags=all=-d=softfloat")
+	}
 	if len(ld) > 0 {
 		flags = append(flags, "-ldflags", strings.Join(ld, " "))
 	}