set H5_PAC_C_MAX_REAL_PRECISION default to 0 when cross compiling with #4299

Job	Run time
Windows MSVC CMake REL TS	10m 52s
Windows MSVC CMake DBG TS	8m 22s
Windows MSVC CMake REL	20m 41s
Windows MSVC CMake DBG	13m 14s
Ubuntu gcc CMake REL TS	4m 18s
Ubuntu gcc CMake DBG TS	3m 25s
Ubuntu gcc CMake REL	10m 33s
Ubuntu gcc CMake DBG	10m 40s
Ubuntu gcc Autotools REL TS	6m 57s
Ubuntu gcc Autotools DBG TS	5m 44s
Ubuntu gcc Autotools REL	16m 51s
Ubuntu gcc Autotools DBG	17m 58s
Ubuntu gcc Autotools parallel (build only) REL TS	6m 1s
Ubuntu gcc Autotools parallel (build only) DBG TS	5m 24s
Ubuntu gcc Autotools parallel (build only) REL	8m 44s
Ubuntu gcc Autotools parallel (build only) DBG	7m 27s
MacOS Clang CMake REL TS	3m 23s
MacOS Clang CMake DBG TS	2m 10s
MacOS Clang CMake REL	8m 36s
MacOS Clang CMake DBG	11m 15s
Ubuntu gcc Autotools v1.6 default API (build only) DBG	9m 21s
Ubuntu gcc Autotools v1.8 default API (build only) DBG	8m 49s
Ubuntu gcc Autotools v1.10 default API (build only) DBG	9m 47s
Ubuntu gcc Autotools v1.12 default API (build only) DBG	8m 51s
Ubuntu gcc Autotools no deprecated symbols (build only) DBG	9m 3s
Ubuntu gcc Autotools -Werror (build only) DBG	7m 16s
Ubuntu gcc Autotools -Werror (build only) REL	7m 57s
Ubuntu gcc Autotools parallel -Werror (build only) DBG	5m 49s
Ubuntu gcc Autotools parallel -Werror (build only) REL	6m 24s
	4h 15m 52s

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