Add EXIT_SUCCESS definition through stdlib.h

[torben-hansen]

Description of changes:

#740 didn't add the definition for EXIT_SUCCESS in the linux_u32 probe.

Call-outs:

This probe was only used for FIPS build. So, it was missed.

Testing:

Before

$ cmake3 [...] -DFIPS=1 ..

[...]

[1/2] Building C object CMakeFiles/cmTC_76f83.dir/linux_u32.c.o
FAILED: CMakeFiles/cmTC_76f83.dir/linux_u32.c.o 
/usr/bin/cc   -std=c99 -fvisibility=hidden -Wall -Wextra -Wno-unused-parameter -Werror -Wunused -Wcomment -Wchar-subscripts -Wuninitialized -Wshadow -Wwrite-strin
gs -Wformat-security -Wunused-result  -Wvla -Wtype-limits -Werror -Wformat=2 -Wsign-compare -Wmissing-field-initializers -Wwrite-strings -ggdb -Wall -fvisibility=
hidden -fno-common -Wno-free-nonheap-object -Wimplicit-fallthrough -Wformat-signedness -Wmissing-prototypes -Wold-style-definition -Wstrict-prototypes    -Werror 
-o CMakeFiles/cmTC_76f83.dir/linux_u32.c.o   -c /home/ec2-user/humble/aws-lc/tests/compiler_features_tests/linux_u32.c
/home/ec2-user/humble/aws-lc/tests/compiler_features_tests/linux_u32.c: In function ‘main’:
/home/ec2-user/humble/aws-lc/tests/compiler_features_tests/linux_u32.c:15:12: compiler_error: ‘EXIT_SUCCESS’ undeclared (first use in this function)
     return EXIT_SUCCESS
            ^~~~~~~~~~~~

[...]

After

No error.

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the ISC license.