Move default crt objects into Toolchain

Move the crt objects spread around cc/library.go and cc/binary.go
into the Toolchain.  This will simplify adding new toolchains that
have custom crt objects.

Test: m checkbuild
Test: go test ./cc/...
Change-Id: I7fdc1f53769799cb9c10e3e5816dabee0f918768
diff --git a/cc/config/arm64_linux_host.go b/cc/config/arm64_linux_host.go
index 59c52d1..83bd799 100644
--- a/cc/config/arm64_linux_host.go
+++ b/cc/config/arm64_linux_host.go
@@ -45,6 +45,16 @@
 		"-Wl,--hash-style=gnu",
 		"-Wl,--no-undefined-version",
 	})
+
+	// Embed the linker into host bionic binaries. This is needed to support host bionic,
+	// as the linux kernel requires that the ELF interpreter referenced by PT_INTERP be
+	// either an absolute path, or relative from CWD. To work around this, we extract
+	// the load sections from the runtime linker ELF binary and embed them into each host
+	// bionic binary, omitting the PT_INTERP declaration. The kernel will treat it as a static
+	// binary, and then we use a special entry point to fix up the arguments passed by
+	// the kernel before jumping to the embedded linker.
+	linuxArm64CrtBeginSharedBinary = append(android.CopyOf(bionicCrtBeginSharedBinary),
+		"host_bionic_linker_script")
 )
 
 func init() {
@@ -68,6 +78,10 @@
 	return "${config.Arm64ClangCflags} ${config.LinuxBionicArm64Cflags}"
 }
 
+func (toolchainLinuxArm64) CrtBeginSharedBinary() []string {
+	return linuxArm64CrtBeginSharedBinary
+}
+
 func linuxArm64ToolchainFactory(arch android.Arch) Toolchain {
 	archVariant := "armv8-a" // for host, default to armv8-a
 	toolchainClangCflags := []string{arm64ClangArchVariantCflagsVar[archVariant]}