bootstrap: add quoting support to avoid splitting

With this change, it is now possible to pass quotes to the configure
script, such as

`./configure.py --set=target.\"thumbv8m.main-none-eabi\".linker=/linker`

, which will treat `thumbv8.main-none-eabi` as a whole part. Currently,
the string would be split into two elements: `thumbv8`, and
`main-none-eabi`.

src/bootstrap/configure.py

@@ -288,8 +288,9 @@ def build(known_args):
 
 def set(key, value, config):
     if isinstance(value, list):
-        # Remove empty values, which value.split(',') tends to generate.
-        value = [v for v in value if v]
+        # Remove empty values, which value.split(',') tends to generate and
+        # replace single quotes for double quotes to ensure correct parsing.
+        value = [v.replace('\'', '"') for v in value if v]
 
     s = "{:20} := {}".format(key, value)
     if len(s) < 70 or VERBOSE:
@@ -298,7 +299,25 @@ def set(key, value, config):
         p(s[:70] + " ...")
 
     arr = config
-    parts = key.split('.')
+
+    # Split on periods unless the block is quoted.
+    parts = []
+    current_part = ''
+    within_quotes = False
+    for character in key:
+        if character in ['"', '\'']:
+            within_quotes = not within_quotes
+        elif character == '.' and not within_quotes:
+            parts.append(current_part)
+            current_part = ''
+        else:
+            current_part += character
+    else:
+        if current_part:
+            parts.append(current_part)
+    if within_quotes:
+        raise RuntimeError('end quote not found in arguments.')
+
     for i, part in enumerate(parts):
         if i == len(parts) - 1:
             if is_value_list(part) and isinstance(value, str):