[PATCH] build: avoid vector performance warnings in randperm

[Pádraig Brady]

* configure.ac: Add -Wno-vector-operation-performance to suppress the
following gcc-9.2 error in gl/lib/randperm.c:
  error: vector operation will be expanded piecewise
---
 configure.ac | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/configure.ac b/configure.ac
index 54af03281..4eab50f1d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -142,6 +142,8 @@ if test "$gl_gcc_warnings" = yes; then
   nw="$nw -Wunsafe-loop-optimizations" # a few src/*.c
   nw="$nw -Winline"                 # system.h's 
readdir_ignoring_dot_and_dotdot
   nw="$nw -Wsuggest-attribute=format" # warns about copy.c and factor.c
+  nw="$nw -Wvector-operation-performance" # warns about randperm.c
+
 
   # Using -Wstrict-overflow is a pain, but the alternative is worse.
   # For an example, see the code that provoked this report:
-- 
2.24.1