Work around Cargo #4866. (#699)

* Work around Cargo build #4866.

This fixes #697.

* Rename "cargo4866workaround" to "core" per review feedback.

cranelift/codegen/Cargo.toml

@@ -26,7 +26,7 @@ log = { version = "0.4.6", default-features = false }
 # accomodated in `tests`.
 
 [build-dependencies]
-cranelift-codegen-meta = { path = "meta", version = "0.30.0" }
+cranelift-codegen-meta = { path = "meta", version = "0.30.0", default-features = false }
 
 [features]
 default = ["std", "x86", "arm32", "arm64", "riscv"]
@@ -34,8 +34,19 @@ default = ["std", "x86", "arm32", "arm64", "riscv"]
 # The "std" feature enables use of libstd. The "core" feature enables use
 # of some minimal std-like replacement libraries. At least one of these two
 # features need to be enabled.
-std = ["cranelift-entity/std", "cranelift-bforest/std", "target-lexicon/std"]
-core = ["hashmap_core"]
+std = [
+    "cranelift-entity/std",
+    "cranelift-bforest/std",
+    "target-lexicon/std",
+    "cranelift-codegen-meta/std"
+]
+
+# The "core" features enables use of "hashmap_core" since core doesn't have
+# a HashMap implementation, and a workaround for Cargo #4866.
+core = [
+    "hashmap_core",
+    "cranelift-codegen-meta/core"
+]
 
 # This enables some additional functions useful for writing tests, but which
 # can significantly increase the size of the library.

cranelift/codegen/meta/Cargo.toml

@@ -9,8 +9,14 @@ readme = "README.md"
 edition = "2018"
 
 [dependencies]
-cranelift-entity = { path = "../../cranelift-entity", version = "0.30.0" }
+cranelift-entity = { path = "../../cranelift-entity", version = "0.30.0", default-features = false }
 
 [badges]
 maintenance = { status = "experimental" }
 travis-ci = { repository = "CraneStation/cranelift" }
+
+[features]
+default = ["std"]
+std = ["cranelift-entity/std"]
+# The "core" feature enables a workaround for Cargo #4866.
+core = ["cranelift-entity/core"]