Fix #1322: replace load-env-vars w/ custom loader

I've replaced load-env-var with our own custom parser. load-env-var
expects a well-formatted env file, which neither env nor set produces,
which is what doom env uses to dump the shell environment.

This should fix issues that arise when envvars (like PATH) contain
arbitrary whitespace.

core/core.el

@@ -427,6 +427,23 @@ in interactive sessions, nil otherwise (but logs a warning)."
          (message "Autoload file warning: %s -> %s" (car e) (error-message-string e))
        (signal 'doom-autoload-error (list (file-name-nondirectory file) e))))))
 
+(defun doom-load-env-vars (file)
+  "Read and set envvars in FILE."
+  (let (vars)
+    (with-temp-buffer
+      (insert-file-contents file)
+      (re-search-forward "\n\n" nil t)
+      (while (re-search-forward "\n\\([^= \n]+\\)=" nil t)
+        (save-excursion
+          (let ((var (match-string 1))
+                (value (buffer-substring-no-properties
+                        (point)
+                        (1- (or (when (re-search-forward "^\\([^= ]+\\)=" nil t)
+                                  (line-beginning-position))
+                                (point-max))))))
+            (setenv var value)))))
+    vars))
+
 (defun doom-initialize (&optional force-p)
   "Bootstrap Doom, if it hasn't already (or if FORCE-P is non-nil).
 
@@ -491,9 +508,8 @@ to least)."
 
     ;; Load shell environment
     (when (and (not noninteractive)
-               (file-readable-p doom-env-file)
-               (require 'load-env-vars nil t))
-      (load-env-vars doom-env-file)
+               (file-readable-p doom-env-file))
+      (doom-load-env-vars doom-env-file)
       (setq exec-path (append (split-string (getenv "PATH") ":")
                               (list exec-directory))
             shell-file-name (or (getenv "SHELL")