attr: Rename the `git_attr__` exports

Pevents collisions with the original libgit, which also exports those
exact symbols.

Fixes #822

include/git2/attr.h

@@ -30,7 +30,7 @@ GIT_BEGIN_DECL
  * Then for file `xyz.c` looking up attribute "foo" gives a value for
  * which `GIT_ATTR_TRUE(value)` is true.
  */
-#define GIT_ATTR_TRUE(attr)		((attr) == git_attr__true)
+#define GIT_ATTR_TRUE(attr)		((attr) == git_l_attr__true)
 
 /**
  * GIT_ATTR_FALSE checks if an attribute is set off.  In core git
@@ -44,7 +44,7 @@ GIT_BEGIN_DECL
  * Then for file `zyx.h` looking up attribute "foo" gives a value for
  * which `GIT_ATTR_FALSE(value)` is true.
  */
-#define GIT_ATTR_FALSE(attr)	((attr) == git_attr__false)
+#define GIT_ATTR_FALSE(attr)	((attr) == git_l_attr__false)
 
 /**
  * GIT_ATTR_UNSPECIFIED checks if an attribute is unspecified.  This
@@ -62,7 +62,7 @@ GIT_BEGIN_DECL
  * file `onefile.rb` or looking up "bar" on any file will all give
  * `GIT_ATTR_UNSPECIFIED(value)` of true.
  */
-#define GIT_ATTR_UNSPECIFIED(attr)	(!(attr) || (attr) == git_attr__unset)
+#define GIT_ATTR_UNSPECIFIED(attr)	(!(attr) || (attr) == git_l_attr__unset)
 
 /**
  * GIT_ATTR_HAS_VALUE checks if an attribute is set to a value (as
@@ -75,12 +75,12 @@ GIT_BEGIN_DECL
  * string "lf" and `GIT_ATTR_SET_TO_VALUE(attr)` will return true.
  */
 #define GIT_ATTR_HAS_VALUE(attr) \
-	((attr) && (attr) != git_attr__unset && \
-	 (attr) != git_attr__true && (attr) != git_attr__false)
+	((attr) && (attr) != git_l_attr__unset && \
+	 (attr) != git_l_attr__true && (attr) != git_attr__false)
 
-GIT_EXTERN(const char *) git_attr__true;
-GIT_EXTERN(const char *) git_attr__false;
-GIT_EXTERN(const char *) git_attr__unset;
+GIT_EXTERN(const char *) git_l_attr__true;
+GIT_EXTERN(const char *) git_l_attr__false;
+GIT_EXTERN(const char *) git_l_attr__unset;
 
 /**
  * Check attribute flags: Reading values from index and working directory.

src/attr_file.c

@@ -5,9 +5,9 @@
 #include "git2/tree.h"
 #include <ctype.h>
 
-const char *git_attr__true  = "[internal]__TRUE__";
-const char *git_attr__false = "[internal]__FALSE__";
-const char *git_attr__unset = "[internal]__UNSET__";
+const char *git_l_attr__true  = "[internal]__TRUE__";
+const char *git_l_attr__false = "[internal]__FALSE__";
+const char *git_l_attr__unset = "[internal]__UNSET__";
 
 static int sort_by_hash_and_name(const void *a_raw, const void *b_raw);
 static void git_attr_rule__clear(git_attr_rule *rule);
@@ -503,14 +503,14 @@ int git_attr_assignment__parse(
 		}
 
 		assign->name_hash = 5381;
-		assign->value = git_attr__true;
+		assign->value = git_l_attr__true;
 
 		/* look for magic name prefixes */
 		if (*scan == '-') {
-			assign->value = git_attr__false;
+			assign->value = git_l_attr__false;
 			scan++;
 		} else if (*scan == '!') {
-			assign->value = git_attr__unset; /* explicit unspecified state */
+			assign->value = git_l_attr__unset; /* explicit unspecified state */
 			scan++;
 		} else if (*scan == '#') /* comment rest of line */
 			break;
@@ -546,7 +546,7 @@ int git_attr_assignment__parse(
 		}
 
 		/* expand macros (if given a repo with a macro cache) */
-		if (repo != NULL && assign->value == git_attr__true) {
+		if (repo != NULL && assign->value == git_l_attr__true) {
 			git_attr_rule *macro =
 				git_attr_cache__lookup_macro(repo, assign->name);