[build] Build user programes with libc++ et al

Adding -lc++ -lc++abi -lunwind to user programs. Also, to support this,
start building using the custom toolchain and its new x86_64-jsix-elf
target triplet.

configs/base.yaml

@@ -1,8 +1,8 @@
 ---
 variables:
-  cc: clang
-  cxx: clang++
-  ld: ld.lld
+  cc: "${source_root}/sysroot/bin/clang"
+  cxx: "${source_root}/sysroot/bin/clang++"
+  ld: "${source_root}/sysroot/bin/ld.lld"
   ar: ar
   nasm: nasm
   objcopy: objcopy

configs/kernel-debug.yaml

@@ -5,7 +5,9 @@ variables:
   asflags: [ "-I${source_root}/src/kernel/" ]
 
   ccflags: [
-    "--target=x86_64-unknown-elf",
+    "--target=x86_64-jsix-elf",
+    "-fno-stack-protector",
+
     "-I${source_root}/external",
 
     "-nostdinc",
@@ -47,6 +49,7 @@ variables:
     "-g",
     "-nostdlib",
     "-Bstatic",
+    "--no-eh-frame-hdr",
     "-z", "norelro",
     "-z", "separate-code" ]
 

configs/user-debug.yaml

@@ -5,8 +5,10 @@ variables:
   asflags: [ "-I${source_root}/src/kernel/" ]
 
   ccflags: [
+    "--target=x86_64-jsix-elf",
     "-mno-sse",
     "-fno-omit-frame-pointer",
+    "-fno-stack-protector",
 
     "-g",
 
@@ -30,5 +32,8 @@ variables:
     "-Bstatic",
     "--sysroot='${source_root}/sysroot'",
     "-L", "${source_root}/sysroot/lib",
-    "-z", "separate-code" ]
+    "-z", "separate-code",
+    "-lc++", "-lc++abi", "-lunwind",
+    "--no-dependent-libraries",
+  ]