Env var for custom C++ compilation flags (#145)

Resolve #144

docs/topic-guides/spec.rst

@@ -92,6 +92,12 @@ A spec file is compiled into a runner program using the following **tcframe** co
 
 The above command will compile ``spec.cpp`` into an executable ``runner`` program in the problem package directory.
 
+It is also possible to specify additional compilation flags, by setting the ``$TCFRAME_CXX_FLAGS`` environment variable. For example:
+
+::
+
+    export TCFRAME_CXX_FLAGS="-Wall -O2"
+
 ----
 
 Runner program

scripts/tcframe

@@ -17,7 +17,7 @@ build() {
         exit 1
     fi
 
-    g++ -std=c++11 -D__TCFRAME_SPEC_FILE__="\"$SPEC_FILE\"" -I "$TCFRAME_HOME/include" -o $RUNNER_EXEC "$TCFRAME_HOME/src/tcframe/runner.cpp"
+    g++ -std=c++11 -D__TCFRAME_SPEC_FILE__="\"$SPEC_FILE\"" -I "$TCFRAME_HOME/include" $TCFRAME_CXX_FLAGS -o $RUNNER_EXEC "$TCFRAME_HOME/src/tcframe/runner.cpp"
 }
 
 version() {

test/ete/resources/library/library.hpp

@@ -0,0 +1 @@
+#pragma once

test/ete/resources/normal/spec.cpp

@@ -1,4 +1,5 @@
 #include <tcframe/spec.hpp>
+#include <library/library.hpp>
 
 using namespace tcframe;
 

test/ete/resources/scripts/generate.sh

@@ -3,6 +3,7 @@
 set -ex
 
 export TCFRAME_HOME=../../tcframe
+export TCFRAME_CXX_FLAGS="-I .."
 
 g++ -o solution solution.cpp
 $TCFRAME_HOME/scripts/tcframe build