[PATCH] Check for fpurge declaration

[Mike Gilbert <floppym@xxxxxxxxxx>]

musl libc defines fpurge, but does not declare it in stdio.h.
It seems to be unnecessary to call fpurge on musl.

Bug: https://bugs.gentoo.org/963567
---
 Src/utils.c  | 2 +-
 configure.ac | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Src/utils.c b/Src/utils.c
index 4ea7b8e93..5e41b712b 100644
--- a/Src/utils.c
+++ b/Src/utils.c
@@ -2022,7 +2022,7 @@ redup(int x, int y)
 {
     int ret = y;
 
-#ifdef HAVE_FPURGE
+#if HAVE_DECL_FPURGE
     /* Make sure buffers are cleared when changing descriptor for a
      * FILE object.  No fflush() here because the only way anything
      * can legitimately be left in the buffer is when an error has
diff --git a/configure.ac b/configure.ac
index 13895bb1d..1f035bc0d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1250,7 +1250,7 @@ AC_CHECK_FUNCS(strftime strptime mktime timelocal \
 	       select poll \
 	       readlink faccessx fchdir ftruncate \
 	       fstat lstat lchown fchown fchmod \
-	       fpurge fseeko ftello \
+	       fseeko ftello \
 	       mkfifo _mktemp mkstemp \
 	       waitpid wait3 \
 	       sigqueue \
@@ -1292,6 +1292,9 @@ AC_CHECK_FUNCS(strftime strptime mktime timelocal \
 	       setutxent getutxent endutxent getutent)
 AC_FUNC_STRCOLL
 
+# fpurge exists on musl, but is undeclared in stdio.h and isn't actually required
+AC_CHECK_DECLS([fpurge])
+
 # isinf() and isnan() can exist as either functions or macros.
 AH_TEMPLATE([HAVE_ISINF],
   [Define to 1 if you have the `isinf' macro or function.])
-- 
2.51.0