gnu: mumble: Fix build with Boost 1.66.

Fixes <https://bugs.gnu.org/31775>.

* gnu/packages/patches/mumble-1.2.19-abs.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/telephony.scm (mumble)[source]: Add it.

gnu/local.mk

@@ -938,6 +938,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/mozjs38-shell-version.patch		\
   %D%/packages/patches/mozjs38-tracelogger.patch		\
   %D%/packages/patches/mozjs38-version-detection.patch		\
+  %D%/packages/patches/mumble-1.2.19-abs.patch			\
   %D%/packages/patches/mumps-build-parallelism.patch		\
   %D%/packages/patches/mupen64plus-ui-console-notice.patch	\
   %D%/packages/patches/mupen64plus-video-z64-glew-correct-path.patch    \

gnu/packages/patches/mumble-1.2.19-abs.patch

@@ -0,0 +1,31 @@
+From ea861fe86743c8402bbad77d8d1dd9de8dce447e Mon Sep 17 00:00:00 2001
+From: Mikkel Krautz <mikkel@krautz.dk>
+Date: Fri, 29 Dec 2017 14:47:25 +0100
+Subject: [PATCH] AudioOutput: do not use non-existant template version of
+ std::abs.
+
+This change fixes AudioOutput to use the float overload of std::abs:
+
+    float std::abs(float);
+
+instead of a non-existant template version (for newer Boost 1.66).
+
+Fixes mumble-voip/mumble#3281
+
+---
+ src/mumble/AudioOutput.cpp | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/mumble/AudioOutput.cpp b/src/mumble/AudioOutput.cpp
+index cbe0c0e2b..7a0a5e2ab 100644
+--- a/src/mumble/AudioOutput.cpp
++++ b/src/mumble/AudioOutput.cpp
+@@ -437,7 +437,7 @@ bool AudioOutput::mix(void *outbuff, unsigned int nsamp) {
+ 					top[2] = 0.0f;
+ 				}
+ 
+-				if (std::abs<float>(front[0] * top[0] + front[1] * top[1] + front[2] * top[2]) > 0.01f) {
++				if (std::abs(front[0] * top[0] + front[1] * top[1] + front[2] * top[2]) > 0.01f) {
+ 					// Not perpendicular. Assume Y up and rotate 90 degrees.
+ 
+ 					float azimuth = 0.0f;

gnu/packages/telephony.scm

@@ -387,6 +387,7 @@ address of one of the participants.")
               (sha256
                (base32
                 "1s60vaici3v034jzzi20x23hsj6mkjlc0glipjq4hffrg9qgnizh"))
+              (patches (search-patches "mumble-1.2.19-abs.patch"))
               (modules '((guix build utils)))
               (snippet
                `(begin