[PATCH] configure: Add sanity checking for environment variables

[David Bremner]

Passing in environment variables incompatible with the compiler may
cause other parts of the configure script to fail in hard to
understand ways, so we abort early.
---

meh, the previous version was borken by lazy evaluation of CXXFLAGS
using make syntax. Better suggestions for how to do this?

 configure | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/configure b/configure
index 4af7ba9..650b976 100755
--- a/configure
+++ b/configure
@@ -269,6 +269,35 @@ dependencies are available:
 EOF
 
 errors=0
+printf "int main(void){return 0;}\n" > minimal.c
+
+printf "Sanity checking C compilation environment... "
+if ${CC} ${CFLAGS} ${CPPFLAGS}  minimal.c ${LDFLAGS} -o minimal > /dev/null 2>&1
+then
+    printf "OK.\n"
+else
+    printf "Fail.\n"
+    errors=$((errors + 1))
+fi
+
+printf "Sanity checking C++ compilation environment... "
+if ${CXX} ${CXXFLAGS_for_sh} ${CPPFLAGS} minimal.c ${LDFLAGS} -o minimal > /dev/null 2>&1
+then
+    printf "OK.\n"
+else
+    printf "Fail.\n"
+    errors=$((errors + 1))
+fi
+
+if [ $errors -gt 0 ]; then
+    cat <<EOF
+*** Error: Initial sanity checking of environment failed.  Please try
+running configure in a clean environment, and if the problem persists,
+report a bug.
+EOF
+    rm -f minimal minimal.c
+    exit 1
+fi
 
 if pkg-config --version > /dev/null 2>&1; then
     have_pkg_config=1
@@ -690,8 +719,6 @@ else
 fi
 rm -f compat/check_asctime
 
-printf "int main(void){return 0;}\n" > minimal.c
-
 printf "Checking for rpath support... "
 if ${CC} -Wl,--enable-new-dtags -Wl,-rpath,/tmp/ -o minimal minimal.c >/dev/null 2>&1
 then
-- 
2.1.4