feaf(makefile) Add the HAS_<compiler> variables.

Makefile

@@ -73,6 +73,9 @@ IS_WINDOWS := 0
 IS_AMD64 := 0
 IS_AARCH64 := 0
 LIBC ?=
+HAS_CRANELIFT := 0
+HAS_LLVM := 0
+HAS_SINGLEPASS := 0
 
 # Test Windows apart because it doesn't support `uname -s`.
 ifeq ($(OS), Windows_NT)
@@ -113,6 +116,7 @@ compilers :=
 ##
 
 compilers += cranelift
+HAS_CRANELIFT := 1
 
 ##
 # LLVM
@@ -137,6 +141,10 @@ else
 	endif
 endif
 
+ifneq (, $(findstring llvm,$(compilers)))
+	HAS_LLVM := 1
+endif
+
 ##
 # Singlepass
 ##
@@ -147,6 +155,10 @@ ifeq ($(IS_WINDOWS), 0)
 	endif
 endif
 
+ifneq (, $(findstring singlepass,$(compilers)))
+	HAS_SINGLEPASS := 1
+endif
+
 
 
 #####
@@ -163,12 +175,14 @@ compilers_engines :=
 # The Cranelift case.
 ##
 
-compilers_engines += cranelift-jit
+ifeq ($(HAS_CRANELIFT, 1))
+	compilers_engines += cranelift-jit
 
-ifeq ($(IS_WINDOWS), 0)
-	ifeq ($(IS_AMD64), 1)
-		ifneq ($(LIBC, musl))
-			compilers_engines += cranelift-native
+	ifeq ($(IS_WINDOWS), 0)
+		ifeq ($(IS_AMD64), 1)
+			ifneq ($(LIBC, musl))
+				compilers_engines += cranelift-native
+			endif
 		endif
 	endif
 endif
@@ -177,8 +191,7 @@ endif
 # The LLVM case.
 ##
 
-# If `compilers` contains `llvm`.
-ifneq (, $(findstring llvm,$(compilers)))
+ifeq ($(HAS_LLVM), 1)
 	ifeq ($(IS_WINDOWS), 0)
 		ifeq ($(IS_AMD64), 1)
 			compilers_engines += llvm-jit
@@ -193,8 +206,7 @@ endif
 # The Singlepass case.
 ##
 
-# If `compilers` contains `singlepass`.
-ifneq (, $(findstring singlepass,$(compilers)))
+ifeq ($(HAS_SINGLEPASS), 1)
 	ifeq ($(IS_WINDOWS), 0)
 		if ($(IS_AMD64), 1)
 			compilers_engines += singlepass-jit