configure: Remove default automake includes

Otherwise we end up masking c++ system headers like <exception> with our
own test and example binaries
diff --git a/configure.ac b/configure.ac
index f0e2e86..399744f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5,7 +5,7 @@
 AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_MACRO_DIRS([m4])
 AC_CONFIG_AUX_DIR([build-aux])
-AM_INIT_AUTOMAKE([foreign subdir-objects -Wall -Werror dist-xz tar-ustar])
+AM_INIT_AUTOMAKE([nostdinc foreign subdir-objects -Wall -Werror dist-xz tar-ustar])
 AM_SILENT_RULES([yes])
 
 # Make sure the default CFLAGS of `-O2 -g` don't override CODE_COVERAGE_CFLAGS