Fix test compiling/execution

Add -fpermissive in %%check to work around invalid conversions in
generated test code. The compiler flags for the installed library are
not changed.

llhttp.spec

@@ -149,8 +149,18 @@ popd
 # code with license problems in the source RPM.
 %{python3} '%{SOURCE3}' --exceptions '%{SOURCE4}' --with dev node_modules_dev
 
+%set_build_flags
+# http-loose-request.c:7205:20: error: invalid conversion from 'void*' to
+#     'const unsigned char*' [-fpermissive]
+#  7205 |     start = state->_span_pos0;
+#       |             ~~~~~~~^~~~~~~~~~
+#       |                    |
+#       |                    void*
+export CXXFLAGS="${CXXFLAGS-} -fpermissive"
+export CFLAGS="${CFLAGS-} -fpermissive"
+export CLANG=gcc
 # See scripts.mocha in package.json:
-NODE_ENV=test CLANG=gcc ./node_modules/.bin/mocha \
+NODE_ENV=test ./node_modules/.bin/mocha \
     -r ts-node/register/type-check \
     test/*-test.ts