Brotli: link against libm.

Change-Id: I19da397875e0aecd7fad15699411df1bb18da6b0
Signed-off-by: Piotr Sikora <piotrsikora@google.com>
Reviewed-on: https://nginx-review.googlesource.com/2480
Reviewed-by: Lizan Zhou <zlizan@google.com>

config

diff --git a/config b/config
index 5194775..2425833 100644
--- a/config
+++ b/config
@@ -65,7 +65,7 @@
 # auto-discovery
 ngx_feature="Brotli library"
 ngx_feature_path=
-ngx_feature_libs="-lbrotlienc"
+ngx_feature_libs="-lbrotlienc -lm"
 . auto/feature
 
 if [ $ngx_found = no ]; then
@@ -73,9 +73,9 @@
     ngx_feature="Brotli library in /usr/local/"
     ngx_feature_path="/usr/local/include"
     if [ $NGX_RPATH = YES ]; then
-        ngx_feature_libs="-R/usr/local/lib -L/usr/local/lib -lbrotlienc"
+        ngx_feature_libs="-R/usr/local/lib -L/usr/local/lib -lbrotlienc -lm"
     else
-        ngx_feature_libs="-L/usr/local/lib -lbrotlienc"
+        ngx_feature_libs="-L/usr/local/lib -lbrotlienc -lm"
     fi
     . auto/feature
 fi
@@ -85,9 +85,9 @@
     ngx_feature="Brotli library in /usr/pkg/"
     ngx_feature_path="/usr/pkg/include"
     if [ $NGX_RPATH = YES ]; then
-        ngx_feature_libs="-R/usr/pkg/lib -L/usr/pkg/lib -lbrotlienc"
+        ngx_feature_libs="-R/usr/pkg/lib -L/usr/pkg/lib -lbrotlienc -lm"
     else
-        ngx_feature_libs="-L/usr/pkg/lib -lbrotlienc"
+        ngx_feature_libs="-L/usr/pkg/lib -lbrotlienc -lm"
     fi
     . auto/feature
 fi
@@ -97,9 +97,9 @@
     ngx_feature="Brotli library in /opt/local/"
     ngx_feature_path="/opt/local/include"
     if [ $NGX_RPATH = YES ]; then
-        ngx_feature_libs="-R/opt/local/lib -L/opt/local/lib -lbrotlienc"
+        ngx_feature_libs="-R/opt/local/lib -L/opt/local/lib -lbrotlienc -lm"
     else
-        ngx_feature_libs="-L/opt/local/lib -lbrotlienc"
+        ngx_feature_libs="-L/opt/local/lib -lbrotlienc -lm"
     fi
     . auto/feature
 fi