posix: define M_PI and other stuff in Zephyr sketches

Author: pillo79

platform.txt

@@ -39,7 +39,7 @@ compiler.define=-DARDUINO=
 compiler.zephyr.includes_file={build.variant.path}/includes.txt
 compiler.zephyr.cflags_file={build.variant.path}/cflags.txt
 compiler.zephyr.cxxflags_file={build.variant.path}/cxxflags.txt
-compiler.zephyr.macros="-imacros{build.variant.path}/llext-edk/include/zephyr/include/generated/zephyr/autoconf.h" "-imacros{build.variant.path}/llext-edk/include/zephyr/include/zephyr/toolchain/zephyr_stdint.h"
+compiler.zephyr.macros="-imacros{build.variant.path}/llext-edk/include/zephyr/include/generated/zephyr/autoconf.h" "-imacros{build.variant.path}/llext-edk/include/zephyr/include/zephyr/toolchain/zephyr_stdint.h" -D_XOPEN_SOURCE=700
 compiler.zephyr.common_cxxflags=-fdata-sections -ffunction-sections -fno-unwind-tables
 compiler.zephyr.common_ldflags=-fno-exceptions -fno-rtti -fno-threadsafe-statics -fno-unwind-tables -fno-use-cxa-atexit -lstdc++ -lsupc++ -lnosys -nostdlib