[libc][stdlib] Simplify getenv_test by using strcmp instead of custom helper

Replace the custom my_streq() helper function with LIBC_NAMESPACE::strcmp(),
simplifying the test code and making it more consistent with other integration
tests in the codebase.

Changes:
- Removed 18-line my_streq() helper function
- Added #include "src/string/strcmp.h"
- Updated string comparisons:
  * Null checks: Direct comparison with nullptr
  * Equality checks: ASSERT_EQ(strcmp(...), 0)
  * Inequality checks: ASSERT_NE(strcmp(...), 0)
- Added libc.src.string.strcmp dependency in CMakeLists.txt

This reduces the test file from 49 to 31 lines while maintaining the same
test coverage. The strcmp-based approach is cleaner and aligns with the
pattern used in the environment_management branch tests (setenv_test,
unsetenv_test, putenv_test).

Testing: Verified that all test assertions pass with the new implementation.

Author: kaladron

libc/test/integration/src/stdlib/CMakeLists.txt

@@ -12,6 +12,7 @@ add_integration_test(
     getenv_test.cpp
   DEPENDS
     libc.src.stdlib.getenv
+    libc.src.string.strcmp
   ENV
     FRANCE=Paris
     GERMANY=Berlin

libc/test/integration/src/stdlib/getenv_test.cpp

@@ -7,43 +7,24 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/stdlib/getenv.h"
+#include "src/string/strcmp.h"
 
 #include "test/IntegrationTest/test.h"
 
-static bool my_streq(const char *lhs, const char *rhs) {
-  if (lhs == rhs)
-    return true;
-  if (((lhs == static_cast<char *>(nullptr)) &&
-       (rhs != static_cast<char *>(nullptr))) ||
-      ((lhs != static_cast<char *>(nullptr)) &&
-       (rhs == static_cast<char *>(nullptr)))) {
-    return false;
-  }
-  const char *l, *r;
-  for (l = lhs, r = rhs; *l != '\0' && *r != '\0'; ++l, ++r)
-    if (*l != *r)
-      return false;
-
-  return *l == '\0' && *r == '\0';
-}
-
 TEST_MAIN([[maybe_unused]] int argc, [[maybe_unused]] char **argv,
           [[maybe_unused]] char **envp) {
-  ASSERT_TRUE(
-      my_streq(LIBC_NAMESPACE::getenv(""), static_cast<char *>(nullptr)));
-  ASSERT_TRUE(
-      my_streq(LIBC_NAMESPACE::getenv("="), static_cast<char *>(nullptr)));
-  ASSERT_TRUE(my_streq(LIBC_NAMESPACE::getenv("MISSING ENV VARIABLE"),
-                       static_cast<char *>(nullptr)));
-  ASSERT_FALSE(
-      my_streq(LIBC_NAMESPACE::getenv("PATH"), static_cast<char *>(nullptr)));
-  ASSERT_TRUE(my_streq(LIBC_NAMESPACE::getenv("FRANCE"), "Paris"));
-  ASSERT_FALSE(my_streq(LIBC_NAMESPACE::getenv("FRANCE"), "Berlin"));
-  ASSERT_TRUE(my_streq(LIBC_NAMESPACE::getenv("GERMANY"), "Berlin"));
-  ASSERT_TRUE(
-      my_streq(LIBC_NAMESPACE::getenv("FRANC"), static_cast<char *>(nullptr)));
-  ASSERT_TRUE(my_streq(LIBC_NAMESPACE::getenv("FRANCE1"),
-                       static_cast<char *>(nullptr)));
+  ASSERT_TRUE(LIBC_NAMESPACE::getenv("") == nullptr);
+  ASSERT_TRUE(LIBC_NAMESPACE::getenv("=") == nullptr);
+  ASSERT_TRUE(LIBC_NAMESPACE::getenv("MISSING ENV VARIABLE") == nullptr);
+  ASSERT_FALSE(LIBC_NAMESPACE::getenv("PATH") == nullptr);
+  ASSERT_EQ(LIBC_NAMESPACE::strcmp(LIBC_NAMESPACE::getenv("FRANCE"), "Paris"),
+            0);
+  ASSERT_NE(LIBC_NAMESPACE::strcmp(LIBC_NAMESPACE::getenv("FRANCE"), "Berlin"),
+            0);
+  ASSERT_EQ(LIBC_NAMESPACE::strcmp(LIBC_NAMESPACE::getenv("GERMANY"), "Berlin"),
+            0);
+  ASSERT_TRUE(LIBC_NAMESPACE::getenv("FRANC") == nullptr);
+  ASSERT_TRUE(LIBC_NAMESPACE::getenv("FRANCE1") == nullptr);
 
   return 0;
 }