configure: tweak test for inline.

It seems that the Brew people are running into a problem.  The
configure test is detecting that "inline" can be used for
declaring inline functions, but then some functions are not
inlined, requiring an external definition.

On GNU/Linuxes, we detect "static inline", so this doesn't
reproduce.

This is likely triggered by the recent change to compile as
C99 (unless configuring in maintainer mode).

* configure: Let's revise the set of possible definitions of
INLINE that we try. Firstly, we only try "inline" if we are
compiling as C++. If that fails, all the other forms of inline
we try include "static". Let's not mess with anything involving
"extern". Like a bare "inline", it might work in the test
program but cause some sort of failure.

1 files changed, 2 insertions, 3 deletions

diff --git a/configure b/configure
index 55fe41eb..9940aa4c 100755
--- a/configure
+++ b/configure
@@ -1528,9 +1528,8 @@ printf "Checking how to declare inline functions ... "
 
 if [ -z "$inline" ] ; then
   for inline in \
-    "inline" "static inline" "extern inline" \
-    "__inline__" "static __inline__" "extern __inline__" \
-    "static"
+    "${cplusplus:+inline}" "static inline" \
+    "static __inline__" "static"
   do
     cat > conftest1.c <<!
 $inline int func(void)