sys-kernel/dracut: fix build on musl

Closes: https://bugs.gentoo.org/847919
Signed-off-by: Mike Gilbert <floppym@gentoo.org>

sys-kernel/dracut/dracut-056.ebuild

@@ -61,6 +61,7 @@ QA_MULTILIB_PATHS="usr/lib/dracut/.*"
 
 PATCHES=(
 	"${FILESDIR}"/gentoo-ldconfig-paths-r1.patch
+	"${FILESDIR}"/056-musl.patch
 )
 
 src_configure() {

sys-kernel/dracut/files/056-musl.patch

@@ -0,0 +1,33 @@
+From ce55a85ed5d902c19d75895508856f96ec2ceb1a Mon Sep 17 00:00:00 2001
+From: Laszlo Gombos <laszlo.gombos@gmail.com>
+Date: Sun, 20 Feb 2022 22:23:49 -0500
+Subject: [PATCH] fix(install): restore musl support
+
+__GLIBC_PREREQ is only defined in glibc.
+---
+ src/install/util.c | 4 +---
+ 1 file changed, 1 insertion(+), 3 deletions(-)
+
+diff --git a/src/install/util.c b/src/install/util.c
+index 5721de89e..0af387c27 100644
+--- a/src/install/util.c
++++ b/src/install/util.c
+@@ -24,17 +24,15 @@
+ #include <errno.h>
+ #include <fcntl.h>
+ #include <sys/types.h>
++#include <sys/syscall.h>
+ 
+ #include "util.h"
+ 
+-#if __GLIBC_PREREQ(2, 30) == 0
+-#include <sys/syscall.h>
+ #ifndef SYS_gettid
+ #error "SYS_gettid unavailable on this system"
+ #endif
+ 
+ #define gettid()    ((pid_t) syscall(SYS_gettid))
+-#endif /*__GLIBC_PREREQ */
+ 
+ size_t page_size(void)
+ {