[libsigcplusplus/libsigc++-2-10] Make --disable-benchmark work

[Murray Cumming <murrayc src gnome org>]

commit 661f12a1e7c21378dc194ce527bdd6c192629481
Author: Christophe Lermytte <gentoo lermytte be>
Date:   Sat Nov 19 23:54:19 2016 +0100

    Make --disable-benchmark work
    
    Currently, when calling ./configure, the possible outcomes of the
    enable_benchmark variable are:
    
    ./configure                          -> ""
    ./configure --enable-benchmark       -> "yes"
    ./configure --enable-benchmark=yes   -> "yes"
    ./configure --enable-benchmark=no    -> "yes"
    ./configure --enable-benchmark=hello -> "yes"
    ./configure --disable-benchmark      -> "yes"
    
    With this commit, those values become
    
    ./configure                          -> ""
    ./configure --enable-benchmark       -> "yes"
    ./configure --enable-benchmark=yes   -> "yes"
    ./configure --enable-benchmark=no    -> "no"
    ./configure --enable-benchmark=hello -> "hello"
    ./configure --disable-benchmark      -> "no"
    
    Note that enable_benchmark is currently only being checked for
    being "yes" or not.
    
    Bug #774732

 configure.ac |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 62deef0..80e8505 100644
--- a/configure.ac
+++ b/configure.ac
@@ -69,8 +69,7 @@ MM_ARG_ENABLE_WARNINGS([SIGC_WXXFLAGS],
 MM_ARG_DISABLE_DEPRECATED_API([SIGCXX])
 
 AC_ARG_ENABLE(benchmark,
-  AS_HELP_STRING([--enable-benchmark=yes|no]),
-  [enable_benchmark=yes]
+  AS_HELP_STRING([--enable-benchmark=yes|no])
 )
 
 AM_CONDITIONAL([SIGC_BUILD_BENCHMARK], [test "x$enable_benchmark" = xyes])