csound: restore patch to fix musl builds

Avoid ugly constructs, thanks.

srcpkgs/csound/patches/musl.patch

@@ -0,0 +1,11 @@
+--- Top/csound.c.orig	2017-07-12 14:54:27.000000000 +0200
++++ Top/csound.c	2017-07-17 17:27:27.064603813 +0200
+@@ -1089,7 +1089,7 @@
+ 
+ static void signal_handler(int sig)
+ {
+-#if defined(LINUX) && !defined(ANDROID) && !defined(NACL)
++#if defined(__GLIBC__)
+     #include <execinfo.h>
+ 
+     {

srcpkgs/csound/template

@@ -19,15 +19,6 @@ distfiles="https://github.com/$pkgname/$pkgname/archive/$version.tar.gz"
 checksum=d49735b4ed50f2818b577abcface45fe7f9b7fb49ccd898db030893cbcdfc738
 nocross=yes
 
-_xreplace() {
-	sed -i "s/$(echo $1 | sed -e 's/\([[\/.*]\|\]\)/\\&/g')/$(echo $2 | sed -e 's/[\/&]/\\&/g')/g" $3
-}
-
-pre_configure() {
-	_xreplace '#if defined(LINUX) && !defined(ANDROID)' '#if defined(__GLIBC__)' \
-		Top/csound.c
-}
-
 post_install() {
 	rm -r $DESTDIR/tmp
 	vinstall ${FILESDIR}/csound.sh 755 etc/profile.d