diff --git a/autoconf/configure.ac b/autoconf/configure.ac
index ff18d69..7d75eb2 100644
--- a/autoconf/configure.ac
+++ b/autoconf/configure.ac
@@ -1080,7 +1080,7 @@
 AC_CHECK_FUNCS([getpagesize getrusage getrlimit setrlimit gettimeofday ])
 AC_CHECK_FUNCS([isatty mkdtemp mkstemp ])
 AC_CHECK_FUNCS([mktemp realpath sbrk setrlimit strdup ])
-AC_CHECK_FUNCS([strerror strerror_r strerror_s ])
+AC_CHECK_FUNCS([strerror strerror_r strerror_s setenv ])
 AC_CHECK_FUNCS([strtoll strtoq sysconf malloc_zone_statistics ])
 AC_CHECK_FUNCS([setjmp longjmp sigsetjmp siglongjmp])
 AC_C_PRINTF_A
diff --git a/cmake/config-ix.cmake b/cmake/config-ix.cmake
index 5b63778..a33e5d9 100755
--- a/cmake/config-ix.cmake
+++ b/cmake/config-ix.cmake
@@ -71,6 +71,7 @@
 check_symbol_exists(strerror string.h HAVE_STRERROR)
 check_symbol_exists(strerror_r string.h HAVE_STRERROR_R)
 check_symbol_exists(strerror_s string.h HAVE_STRERROR_S)
+check_symbol_exists(setenv stdlib.h HAVE_SETENV)
 
 check_symbol_exists(__GLIBC__ stdio.h LLVM_USING_GLIBC)
 if( LLVM_USING_GLIBC )
diff --git a/configure b/configure
index 28a3cfe..9954f94 100755
--- a/configure
+++ b/configure
@@ -32291,7 +32291,8 @@
 
 
 
-for ac_func in strerror strerror_r strerror_s
+
+for ac_func in strerror strerror_r strerror_s setenv
 do
 as_ac_var=`echo "ac_cv_func_$ac_func" | $as_tr_sh`
 { echo "$as_me:$LINENO: checking for $ac_func" >&5
diff --git a/include/llvm/Config/config.h.cmake b/include/llvm/Config/config.h.cmake
index 360ca5d..d8de146 100644
--- a/include/llvm/Config/config.h.cmake
+++ b/include/llvm/Config/config.h.cmake
@@ -291,6 +291,9 @@
 /* Define to 1 if you have the `sbrk' function. */
 #undef HAVE_SBRK
 
+/* Define to 1 if you have the `setenv' function. */
+#cmakedefine HAVE_SETENV ${HAVE_SETENV}
+
 /* Define to 1 if you have the `setjmp' function. */
 #undef HAVE_SETJMP
 
diff --git a/include/llvm/Config/config.h.in b/include/llvm/Config/config.h.in
index f32f403..5257df9 100644
--- a/include/llvm/Config/config.h.in
+++ b/include/llvm/Config/config.h.in
@@ -321,6 +321,9 @@
 /* Define to 1 if you have the `sbrk' function. */
 #undef HAVE_SBRK
 
+/* Define to 1 if you have the `setenv' function. */
+#undef HAVE_SETENV
+
 /* Define to 1 if you have the `setjmp' function. */
 #undef HAVE_SETJMP
 
diff --git a/unittests/Support/CommandLineTest.cpp b/unittests/Support/CommandLineTest.cpp
index 70d6950..72fa24a 100644
--- a/unittests/Support/CommandLineTest.cpp
+++ b/unittests/Support/CommandLineTest.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Config/config.h"
 
 #include "gtest/gtest.h"
 
@@ -24,17 +25,26 @@
       : name(name) {
     const char *old_value = getenv(name);
     EXPECT_EQ(NULL, old_value) << old_value;
+#if HAVE_SETENV
     setenv(name, value, true);
+#else
+#   define SKIP_ENVIRONMENT_TESTS
+#endif
   }
 
   ~TempEnvVar() {
+#if HAVE_SETENV
+    // Assume setenv and unsetenv come together.
     unsetenv(name);
+#endif
   }
 
  private:
   const char *const name;
 };
 
+#ifndef SKIP_ENVIRONMENT_TESTS
+
 const char test_env_var[] = "LLVM_TEST_COMMAND_LINE_FLAGS";
 
 cl::opt<std::string> EnvironmentTestOption("env-test-opt");
@@ -45,4 +55,6 @@
   EXPECT_EQ("hello", EnvironmentTestOption);
 }
 
+#endif  // SKIP_ENVIRONMENT_TESTS
+
 }  // anonymous namespace