Fix risc-v build

Two fixes in one:

Firstly, replace non-standard __uint64_t with standard (but optional) uint64_t.
__uint64_t is not a part of C standard; it is defined by some platforms but might not
be present in every environment (e.g. in freestanding build). On the other hand, uint64_t
is standard C. It is optional but virtual guaranteed to be present for any 32/64 bit machine.

Secondly, mark riscv64 for 128-bit long double in make/cmake files. This fixes cmake
build (which detects presence of long double and tries to compile extended functions),
and brings make build to do the same.

CMakeLists.txt

@@ -551,7 +551,7 @@ list(APPEND OPENLIBM_INCLUDE_DIRS
 if(${OPENLIBM_ARCH_FOLDER} STREQUAL "i387" OR ${OPENLIBM_ARCH_FOLDER} STREQUAL "amd64" OR ${OPENLIBM_ARCH_FOLDER} STREQUAL "powerpc")
     list(APPEND OPENLIBM_INCLUDE_DIRS "${PROJECT_SRC}/ld80")
 else()
-    if(${OPENLIBM_ARCH_FOLDER} STREQUAL "aarch64")
+    if(${OPENLIBM_ARCH_FOLDER} STREQUAL "aarch64" OR ${OPENLIBM_ARCH_FOLDER} STREQUAL "riscv64")
         list(APPEND OPENLIBM_INCLUDE_DIRS "${PROJECT_SRC}/ld128")
     endif()
 endif()

Make.inc

@@ -155,7 +155,7 @@ CFLAGS_add += -std=c99 -Wall -I$(OPENLIBM_HOME) -I$(OPENLIBM_HOME)/include -I$(O
 ifneq ($(filter $(ARCH),i387 amd64 powerpc),)
 CFLAGS_add += -I$(OPENLIBM_HOME)/ld80
 else
-ifneq ($(filter $(ARCH),aarch64),)
+ifneq ($(filter $(ARCH),aarch64 riscv64),)
 CFLAGS_add += -I$(OPENLIBM_HOME)/ld128
 endif
 endif
@@ -165,7 +165,7 @@ ifneq ($(filter $(ARCH),i387 amd64),)
 # linux x86_64, for instance, `long double` is 80 bits wide, whereas on macOS aarch64,
 # `long double` is the same as `double`. 
 LONG_DOUBLE_NOT_DOUBLE := 1
-else ifeq ($(ARCH), aarch64)
+else ifeq ($(ARCH), aarch64 riscv64)
 ifeq ($(filter $(OS),Darwin WINNT),)
 LONG_DOUBLE_NOT_DOUBLE := 1
 endif

include/openlibm_fenv_riscv.h

@@ -45,8 +45,8 @@
 #define	__fenv_static	static
 #endif
 
-typedef	__uint64_t	fenv_t;
-typedef	__uint64_t	fexcept_t;
+typedef	uint64_t	fenv_t;
+typedef	uint64_t	fexcept_t;
 
 /* Exception flags */
 #define	FE_INVALID	0x0010