[libc] Fix GPU tests failing after recent changes

[jhuber6]

Summary

Summray:
We landed some extra math support, which is apparently broken on the
max / min functions. the mod functions cannot be tested as they use
std::limits which don't exist in a freestanding environment. Also the
blockstore test seems to be broken. We will need to fix these in the
future but for now we need something in a workable state.

[jplehr]

LGTM

libc/test/src/__support/CMakeLists.txt

 add_custom_target(libc-support-tests)
 
+# FIXME: These tests are currently broken on the GPU.
+if(NOT LIBC_TARGET_ARCHITECTURE_IS_GPU)
   add_libc_test(
     blockstore_test
     SUITE
       libc-support-tests
     SRCS
       blockstore_test.cpp
     DEPENDS
       libc.src.__support.blockstore
   )
+endif()
 
 add_libc_test(
   endian_test
   SUITE
     libc-support-tests
   SRCS
     endian_test.cpp
   DEPENDS

libc/test/src/math/CMakeLists.txt

SRCS
     modf_test.cpp
   HDRS
     ModfTest.h
   DEPENDS
     libc.include.math
     libc.src.math.modf
     libc.src.__support.FPUtil.basic_operations
     libc.src.__support.FPUtil.nearest_integer_operations
+  # Requires C++ limits.
+  UNIT_TEST_ONLY
 )
 
 add_fp_unittest(
   modff_test
   SUITE
     libc_math_unittests
   SRCS
     modff_test.cpp
   HDRS
     ModfTest.h
   DEPENDS
     libc.include.math
     libc.src.math.modff
     libc.src.__support.FPUtil.basic_operations
     libc.src.__support.FPUtil.nearest_integer_operations
+  # Requires C++ limits.
+  UNIT_TEST_ONLY
 )
 
 add_fp_unittest(
   modfl_test
   SUITE
     libc_math_unittests
   SRCS
     modfl_test.cpp
HDRS
     FDimTest.h
   DEPENDS
     libc.include.math
     libc.src.math.fdiml
     libc.src.__support.FPUtil.basic_operations
     libc.src.__support.FPUtil.fp_bits
 )
 
+# FIXME: These tests are currently broken on the GPU.
+if(NOT LIBC_TARGET_ARCHITECTURE_IS_GPU)
   add_fp_unittest(
     fminf_test
     SUITE
       libc_math_unittests
     SRCS
       fminf_test.cpp
     HDRS
       FMinTest.h
     DEPENDS
       libc.include.math
       libc.src.math.fminf
       libc.src.__support.FPUtil.fp_bits
   )
 
   add_fp_unittest(
     fmin_test
     SUITE
       libc_math_unittests
     SRCS
       fmin_test.cpp
     HDRS
       FMinTest.h
     DEPENDS
       libc.include.math
       libc.src.math.fmin
       libc.src.__support.FPUtil.fp_bits
   )
 
   add_fp_unittest(
     fminl_test
     SUITE
       libc_math_unittests
     SRCS
       fminl_test.cpp
     HDRS
       FMinTest.h
     DEPENDS
       libc.include.math
       libc.src.math.fminl
       libc.src.__support.FPUtil.fp_bits
   )
 
   add_fp_unittest(
     fmaxf_test
     SUITE
       libc_math_unittests
     SRCS
       fmaxf_test.cpp
     HDRS
       FMaxTest.h
     DEPENDS
       libc.include.math
       libc.src.math.fmaxf
       libc.src.__support.FPUtil.fp_bits
   )
 
   add_fp_unittest(
     fmax_test
     SUITE
       libc_math_unittests
     SRCS
       fmax_test.cpp
     HDRS
       FMaxTest.h
     DEPENDS
       libc.include.math
       libc.src.math.fmax
       libc.src.__support.FPUtil.fp_bits
   )
 
   add_fp_unittest(
     fmaxl_test
     SUITE
       libc_math_unittests
     SRCS
       fmaxl_test.cpp
     HDRS
       FMaxTest.h
     DEPENDS
       libc.include.math
       libc.src.math.fmaxl
       libc.src.__support.FPUtil.fp_bits
   )
+endif()
 
 add_fp_unittest(
   sqrtf_test
   NEED_MPFR
   SUITE
     libc_math_unittests
   SRCS
     sqrtf_test.cpp
add_fp_unittest(
   HDRS
     FModTest.h
   DEPENDS
     libc.include.math
     libc.src.errno.errno
     libc.src.math.fmodf
     libc.src.__support.FPUtil.basic_operations
     libc.src.__support.FPUtil.nearest_integer_operations
+  # Requires C++ limits.
+  UNIT_TEST_ONLY
 )
 
 add_fp_unittest(
   fmod_test
   SUITE
     libc_math_unittests
   SRCS
     fmod_test.cpp
   HDRS
     FModTest.h
   DEPENDS
     libc.include.math
     libc.src.errno.errno
     libc.src.math.fmod
     libc.src.__support.FPUtil.basic_operations
     libc.src.__support.FPUtil.nearest_integer_operations
+  # Requires C++ limits.
+  UNIT_TEST_ONLY
 )
 
 add_fp_unittest(
   explogxf_test
   NEED_MPFR
   SUITE
     libc_math_unittests
   HDRS