Reland "[flang][runtime] Enable I/O APIs in F18 runtime offload builds." (#87729)

This reverts commit 22089ae.

Author: vzakhari

flang/include/flang/Runtime/io-api.h

@@ -49,6 +49,7 @@ static void SetEnvironmentDefaults(const EnvironmentDefaultList *envDefaults) {
   }
 }
 
+RT_OFFLOAD_API_GROUP_BEGIN
 Fortran::common::optional<Convert> GetConvertFromString(
     const char *x, std::size_t n) {
   static const char *keywords[]{
@@ -68,6 +69,7 @@ Fortran::common::optional<Convert> GetConvertFromString(
     return Fortran::common::nullopt;
   }
 }
+RT_OFFLOAD_API_GROUP_END
 
 void ExecutionEnvironment::Configure(int ac, const char *av[],
     const char *env[], const EnvironmentDefaultList *envDefaults) {

flang/runtime/environment.cpp

@@ -31,7 +31,7 @@ RT_OFFLOAD_VAR_GROUP_END
 // External unformatted I/O data conversions
 enum class Convert { Unknown, Native, LittleEndian, BigEndian, Swap };
 
-Fortran::common::optional<Convert> GetConvertFromString(
+RT_API_ATTRS Fortran::common::optional<Convert> GetConvertFromString(
     const char *, std::size_t);
 
 struct ExecutionEnvironment {

flang/runtime/environment.h

@@ -52,6 +52,11 @@
 #define STD_STRCPY_UNSUPPORTED 1
 #endif
 
+#if !defined(STD_STRCMP_UNSUPPORTED) && \
+    (defined(__CUDACC__) || defined(__CUDA__)) && defined(__CUDA_ARCH__)
+#define STD_STRCMP_UNSUPPORTED 1
+#endif
+
 namespace Fortran::runtime {
 
 #if STD_FILL_N_UNSUPPORTED
@@ -176,5 +181,19 @@ static inline RT_API_ATTRS char *strcpy(char *dest, const char *src) {
 using std::strcpy;
 #endif // !STD_STRCPY_UNSUPPORTED
 
+#if STD_STRCMP_UNSUPPORTED
+// Provides alternative implementation for std::strcmp(), if
+// it is not supported.
+static inline RT_API_ATTRS int strcmp(const char *lhs, const char *rhs) {
+  while (*lhs != '\0' && *lhs == *rhs) {
+    ++lhs;
+    ++rhs;
+  }
+  return static_cast<unsigned char>(*lhs) - static_cast<unsigned char>(*rhs);
+}
+#else // !STD_STRCMP_UNSUPPORTED
+using std::strcmp;
+#endif // !STD_STRCMP_UNSUPPORTED
+
 } // namespace Fortran::runtime
 #endif // FORTRAN_RUNTIME_FREESTANDING_TOOLS_H_