Fix builds with GCC on Windows

[vhotspur]

Using the default Windows configuration for GitHub Actions ends with the following bug:

compile-agent-gcc:
    [apply] D:\a\java-ubench-agent\java-ubench-agent\src\c\events.c: In function 'getter_thread_time':
    [apply] D:\a\java-ubench-agent\java-ubench-agent\src\c\events.c:96:60: warning: unused parameter 'bench' [-Wunused-parameter]
    [apply]    96 | static long long getter_thread_time(const benchmark_run_t *bench, const ubench_event_info_t *UNUSED_PARAMETER(info)) {
    [apply]       |                                     ~~~~~~~~~~~~~~~~~~~~~~~^~~~~
    [apply] In file included from D:\a\java-ubench-agent\java-ubench-agent\src\c\jnifunc.c:22:
    [apply] D:\a\java-ubench-agent\java-ubench-agent\src\c\jnifunc.c: In function 'Java_cz_cuni_mff_d3s_perf_NativeThreads_getNativeId':
    [apply] D:\a\java-ubench-agent\java-ubench-agent\out\agent/cz_cuni_mff_d3s_perf_NativeThreads.h:11:63: error: invalid suffix "i64" on integer constant
    [apply]    11 | #define cz_cuni_mff_d3s_perf_NativeThreads_INVALID_THREAD_ID -1i64
    [apply]       |                                                               ^~~~
    [apply] D:\a\java-ubench-agent\java-ubench-agent\src\c\jnifunc.c:39:32: note: in expansion of macro 'cz_cuni_mff_d3s_perf_NativeThreads_INVALID_THREAD_ID'
    [apply]    39 |                 return (jlong) cz_cuni_mff_d3s_perf_NativeThreads_INVALID_THREAD_ID;
    [apply]       |                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Probably caused by javah generating MSVC-specific header as i64 suffix is a non-standard MS extension.

[lbulej]

Probably caused by javah generating MSVC-specific header as i64 suffix is a non-standard MS extension.

I observed this recently as well when I was sharing the same development tree between Linux and Windows. Using javah on windows produces such header files, making the agent impossible to compile on linux. ant clean fixed the problem.