Patch that fixes toplevel.{c,h} defines of {floor,exact}_log2
aur-general discussion: https://lists.archlinux.org/pipermail/aur-general/2015-June/031034.html
Made by 'carstene1ns'
References, taken from above mail:
[1]: https://paste.xinu.at/f32k/ # This patch
[2]: https://gcc.gnu.org/gcc-5/porting_to.html ("Different semantics for
inline functions")
[3]: https://github.com/gcc-mirror/gcc/commit/4345dfaa7260253cb0d3b10b4b466f586e9d28dc
diff -Npur a/gcc/toplev.c b/gcc/toplev.c
--- a/gcc/toplev.c	2010-03-31 04:51:31.000000000 +0200
+++ b/gcc/toplev.c	2015-06-21 20:23:54.025339943 +0200
@@ -523,11 +523,11 @@ read_integral_parameter (const char *p,
   return atoi (p);
 }

-/* When compiling with a recent enough GCC, we use the GNU C "extern inline"
-   for floor_log2 and exact_log2; see toplev.h.  That construct, however,
-   conflicts with the ISO C++ One Definition Rule.   */
+/* The functions floor_log2 and exact_log2 are defined as inline
+   functions in toplev.h if GCC_VERSION >= 3004.  The definitions here
+   are used for older versions of gcc.  */

-#if GCC_VERSION < 3004 || !defined (__cplusplus)
+#if GCC_VERSION < 3004

 /* Given X, an unsigned number, return the largest int Y such that 2**Y <= X.
    If X is 0, return -1.  */
@@ -540,9 +540,6 @@ floor_log2 (unsigned HOST_WIDE_INT x)
   if (x == 0)
     return -1;

-#ifdef CLZ_HWI
-  t = HOST_BITS_PER_WIDE_INT - 1 - (int) CLZ_HWI (x);
-#else
   if (HOST_BITS_PER_WIDE_INT > 64)
     if (x >= (unsigned HOST_WIDE_INT) 1 << (t + 64))
       t += 64;
@@ -559,7 +556,6 @@ floor_log2 (unsigned HOST_WIDE_INT x)
     t += 2;
   if (x >= ((unsigned HOST_WIDE_INT) 1) << (t + 1))
     t += 1;
-#endif

   return t;
 }
@@ -572,14 +568,10 @@ exact_log2 (unsigned HOST_WIDE_INT x)
 {
   if (x != (x & -x))
     return -1;
-#ifdef CTZ_HWI
-  return x ? CTZ_HWI (x) : -1;
-#else
   return floor_log2 (x);
-#endif
 }

-#endif /*  GCC_VERSION < 3004 || !defined (__cplusplus)  */
+#endif /*  GCC_VERSION < 3004 */

 /* Handler for fatal signals, such as SIGSEGV.  These are transformed
    into ICE messages, which is much more user friendly.  In case the
diff -Npur a/gcc/toplev.h b/gcc/toplev.h
--- a/gcc/toplev.h	2009-02-20 16:20:38.000000000 +0100
+++ b/gcc/toplev.h	2015-06-21 20:24:35.142568303 +0200
@@ -167,14 +167,17 @@ extern void decode_d_option		(const char
 extern bool fast_math_flags_set_p	(void);
 extern bool fast_math_flags_struct_set_p (struct cl_optimization *);

+#if GCC_VERSION < 3004
+
 /* Return log2, or -1 if not exact.  */
 extern int exact_log2                  (unsigned HOST_WIDE_INT);

 /* Return floor of log2, with -1 for zero.  */
 extern int floor_log2                  (unsigned HOST_WIDE_INT);

+#else /* GCC_VERSION >= 3004 */
+
 /* Inline versions of the above for speed.  */
-#if GCC_VERSION >= 3004
 # if HOST_BITS_PER_WIDE_INT == HOST_BITS_PER_LONG
 #  define CLZ_HWI __builtin_clzl
 #  define CTZ_HWI __builtin_ctzl
@@ -186,17 +189,18 @@ extern int floor_log2                  (
 #  define CTZ_HWI __builtin_ctz
 # endif

-extern inline int
+static inline int
 floor_log2 (unsigned HOST_WIDE_INT x)
 {
   return x ? HOST_BITS_PER_WIDE_INT - 1 - (int) CLZ_HWI (x) : -1;
 }

-extern inline int
+static inline int
 exact_log2 (unsigned HOST_WIDE_INT x)
 {
   return x == (x & -x) && x ? (int) CTZ_HWI (x) : -1;
 }
+
 #endif /* GCC_VERSION >= 3004 */

 /* Functions used to get and set GCC's notion of in what directory