[libc] Reduce direct use of errno in src/stdlib and src/__support tests. (llvm#143767)

* Get rid of libc_errno assignments in str_to_* __support tests, since
those API have been migrated to return error in a struct instead.
* Migrate tests for atof and to strto* functions from <stdlib.h> and for
strdup from <string.h> to use ErrnoCheckingTest harness.

Author: vonosmas

libc/test/src/__support/CMakeLists.txt

@@ -127,7 +127,6 @@ add_libc_test(
     libc.src.__support.integer_literals
     libc.src.__support.str_to_float
     libc.src.__support.uint128
-    libc.src.errno.errno
 )
 
 
@@ -140,7 +139,6 @@ add_libc_test(
   DEPENDS
     libc.src.__support.integer_literals
     libc.src.__support.str_to_integer
-    libc.src.errno.errno
 )
 
 add_libc_test(

libc/test/src/__support/str_to_double_test.cpp

@@ -99,7 +99,6 @@ TEST(LlvmLibcStrToDblTest, SimpleDecimalConversionExtraTypes) {
   uint64_t double_output_mantissa = 0;
   uint32_t output_exp2 = 0;
 
-  LIBC_NAMESPACE::libc_errno = 0;
   auto double_result =
       internal::simple_decimal_conversion<double>("123456789012345678900");
 

libc/test/src/__support/str_to_float_test.cpp

@@ -55,7 +55,6 @@ TEST(LlvmLibcStrToFltTest, SimpleDecimalConversionExtraTypes) {
   uint32_t float_output_mantissa = 0;
   uint32_t output_exp2 = 0;
 
-  LIBC_NAMESPACE::libc_errno = 0;
   auto float_result =
       internal::simple_decimal_conversion<float>("123456789012345678900");
   float_output_mantissa = float_result.num.mantissa;

libc/test/src/__support/str_to_fp_test.h

@@ -10,7 +10,6 @@
 #include "src/__support/macros/config.h"
 #include "src/__support/str_to_float.h"
 #include "src/__support/uint128.h"
-#include "src/errno/libc_errno.h"
 
 #include "test/UnitTest/Test.h"
 
@@ -67,7 +66,6 @@ template <typename T> struct LlvmLibcStrToFloatTest : public testing::Test {
                                       const int expectedErrno = 0) {
     StorageType actual_output_mantissa = 0;
     uint32_t actual_output_exp2 = 0;
-    LIBC_NAMESPACE::libc_errno = 0;
 
     auto result = internal::simple_decimal_conversion<T>(numStart);
 

libc/test/src/__support/str_to_integer_test.cpp

@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/__support/str_to_integer.h"
-#include "src/errno/libc_errno.h"
 #include <stddef.h>
 
 #include "test/UnitTest/Test.h"

libc/test/src/stdlib/CMakeLists.txt

@@ -9,6 +9,7 @@ add_libc_test(
   DEPENDS
     libc.src.errno.errno
     libc.src.stdlib.atof
+    libc.test.UnitTest.ErrnoCheckingTest
 )
 
 add_header_library(
@@ -64,6 +65,7 @@ add_fp_unittest(
     libc.src.errno.errno
     libc.src.stdlib.strtod
     libc.src.__support.FPUtil.fenv_impl
+    libc.test.UnitTest.ErrnoCheckingTest
 )
 
 add_fp_unittest(
@@ -76,6 +78,7 @@ add_fp_unittest(
     libc.src.errno.errno
     libc.src.stdlib.strtof
     libc.src.__support.FPUtil.fenv_impl
+    libc.test.UnitTest.ErrnoCheckingTest
 )
 
 add_header_library(
@@ -86,6 +89,7 @@ add_header_library(
     libc.src.__support.CPP.limits
     libc.src.__support.CPP.type_traits
     libc.src.errno.errno
+    libc.test.UnitTest.ErrnoCheckingTest
 )
 
 add_libc_test(
@@ -133,6 +137,7 @@ add_libc_test(
     libc.src.errno.errno
     libc.src.__support.uint128
     libc.src.stdlib.strtold
+    libc.test.UnitTest.ErrnoCheckingTest
 )
 
 add_libc_test(