targets: make compiler runtime selection more configurable

main.go

@@ -153,7 +153,7 @@ func Compile(pkgName, outpath string, spec *TargetSpec, config *BuildConfig, act
 		// Load builtins library from the cache, possibly compiling it on the
 		// fly.
 		var cachePath string
-		if spec.CompilerRT {
+		if spec.RTLib == "compiler-rt" {
 			librt, err := loadBuiltins(spec.Triple)
 			if err != nil {
 				return err
@@ -165,7 +165,7 @@ func Compile(pkgName, outpath string, spec *TargetSpec, config *BuildConfig, act
 		executable := filepath.Join(dir, "main")
 		tmppath := executable // final file
 		args := append(spec.PreLinkArgs, "-o", executable, objfile)
-		if spec.CompilerRT {
+		if spec.RTLib == "compiler-rt" {
 			args = append(args, "-L", cachePath, "-lrt-"+spec.Triple)
 		}
 		cmd := exec.Command(spec.Linker, args...)

target.go

@@ -20,7 +20,7 @@ type TargetSpec struct {
 	Triple      string   `json:"llvm-target"`
 	BuildTags   []string `json:"build-tags"`
 	Linker      string   `json:"linker"`
-	CompilerRT  bool     `json:"compiler-rt"`
+	RTLib       string   `json:"rtlib"` // compiler runtime library (libgcc, compiler-rt)
 	PreLinkArgs []string `json:"pre-link-args"`
 	Objcopy     string   `json:"objcopy"`
 	Emulator    []string `json:"emulator"`

targets/bluepill.json

@@ -2,7 +2,7 @@
 	"llvm-target": "armv7m-none-eabi",
 	"build-tags": ["bluepill", "stm32f103xx", "stm32", "tinygo.arm", "js", "wasm"],
 	"linker": "arm-none-eabi-gcc",
-	"compiler-rt": true,
+	"rtlib": "compiler-rt",
 	"pre-link-args": ["-nostdlib", "-nostartfiles", "-mcpu=cortex-m3", "-mthumb", "-T", "targets/stm32.ld", "-Wl,--gc-sections", "-fno-exceptions", "-fno-unwind-tables", "-ffunction-sections", "-fdata-sections", "-Os", "src/device/stm32/stm32f103xx.s"],
 	"objcopy": "arm-none-eabi-objcopy",
 	"flash": "openocd -f interface/stlink-v2.cfg -f target/stm32f1x.cfg -c 'program {hex} reset exit'"

targets/microbit.json

@@ -2,7 +2,7 @@
 	"llvm-target": "armv6m-none-eabi",
 	"build-tags": ["microbit", "nrf51822", "nrf51", "nrf", "tinygo.arm", "js", "wasm"],
 	"linker": "arm-none-eabi-gcc",
-	"compiler-rt": true,
+	"rtlib": "compiler-rt",
 	"pre-link-args": [
 		"-nostdlib",
 		"-nostartfiles",

targets/pca10040.json

@@ -2,7 +2,7 @@
 	"llvm-target": "armv7em-none-eabi",
 	"build-tags": ["pca10040", "nrf52832", "nrf52", "nrf", "tinygo.arm", "js", "wasm"],
 	"linker": "arm-none-eabi-gcc",
-	"compiler-rt": true,
+	"rtlib": "compiler-rt",
 	"pre-link-args": [
 		"-nostdlib",
 		"-nostartfiles",

targets/qemu.json

@@ -2,7 +2,7 @@
 	"llvm-target": "armv7m-none-eabi",
 	"build-tags": ["qemu", "lm3s6965", "tinygo.arm", "js", "wasm"],
 	"linker": "arm-none-eabi-gcc",
-	"compiler-rt": true,
+	"rtlib": "compiler-rt",
 	"pre-link-args": [
 		"-nostdlib",
 		"-nostartfiles",