dist/tools: add check for extern "C" declaration

dist/tools/externc/check.sh

@@ -0,0 +1,37 @@
+#!/bin/sh
+
+# customizable
+CHECKROOT=$(dirname "${0}")
+
+# prepare
+ROOT=$(git rev-parse --show-toplevel)
+EXIT_CODE=0
+BRANCH="${1}"
+DIFFFILTER="${2}"
+
+# set default diff-filter
+if [ -z "${DIFFFILTER}" ]; then
+    DIFFFILTER="ACMR"
+fi
+
+# select files to check
+if [ -z "${BRANCH}" ]; then
+    FILES="$(git ls-tree -r --full-tree --name-only HEAD | grep -E '\.h$')"
+else
+    FILES="$(git diff --diff-filter=${DIFFFILTER} --name-only ${BRANCH} | grep -E '\.h$')"
+fi
+
+# check files
+for FILE in ${FILES}; do
+    if head -100 "${ROOT}/${FILE}" \
+        | sed -e 's/$/ /' \
+        | tr -d '\r\n' \
+        | sed -e 's/  */ /g' \
+        | grep -v -q '#ifdef __cplusplus extern "C" { #endif'; \
+    then
+        EXIT_CODE=1
+        echo "file does not have a C++ compatible header: '${FILE}'"
+    fi
+done
+
+exit ${EXIT_CODE}