Function test_snprintf() is called by run_test_snprintf() with constant test
data. It gets inlined and is subjected to snprintf format truncation checks
introduced by -Wformat-truncation in gcc-7. -Wformat-truncation is turned
On by -Wall and other similar options. It results in error with -Werror.
-Wformat-truncation makes tests performed by run_test_snprintf() redundant
on gcc. But they are still relevant for other compilers. This commit prevents
inlining of test_snprintf() to avoid gcc compile time checks.
