Add RISC-V to cmake linux (scp-fs2open#6375)

* Add support for RISC-V compile to cmake

* No need to pass -march for gcc in riscv

* -march=native is not supported in Risc-V clang

* fix comment and remove unnecessary newline

* Remove incorrect values while checking CMAKE_SYSTEM_PROCESSOR

* Support 32bit RISCV as well

I dont think this will be ever be needed, but i dont like that compilation will fail due to incorrect compiler flags if you try.

cmake/globals.cmake

@@ -19,3 +19,15 @@ else()
         set(IS_ARM64 TRUE)
     endif()
 endif()
+
+set(IS_RISCV FALSE)
+
+if (NOT "${CMAKE_GENERATOR_PLATFORM}" STREQUAL "")   # needed to cover Visual Studio generator
+    if(CMAKE_GENERATOR_PLATFORM MATCHES "^(riscv64|RISCV64|riscv32|RISCV32)")
+        set(IS_RISCV TRUE)
+    endif()
+else()
+    if(CMAKE_SYSTEM_PROCESSOR MATCHES "^(riscv64|RISCV64|riscv32|RISCV32)")
+        set(IS_RISCV TRUE)
+    endif()
+endif()

cmake/platformChecks.h.in

@@ -10,6 +10,7 @@
 
 #cmakedefine01 IS_64BIT
 #cmakedefine01 IS_ARM64
+#cmakedefine01 IS_RISCV
 
 #cmakedefine01 SCP_HAVE_STRCASECMP
 #cmakedefine01 SCP_HAVE_STRNCASECMP

cmake/toolchain-clang.cmake

@@ -9,9 +9,17 @@ option(CLANG_ENABLE_ADDRESS_SANITIZER "Enable -fsanitize=address" OFF)
 
 option(CLANG_USE_LIBCXX "Use libc++" OFF)
 
-# These are the default values
-set(C_BASE_FLAGS "-march=native -pipe")
-set(CXX_BASE_FLAGS "-march=native -pipe")
+# Clang does not support -march=native for RISC-V
+if(IS_RISCV)
+	# You do not need to pass a -march, passing nothing will make clang to choose itself.
+	# If you want a specific set of instructions like vectors, set -march in CFLAGS and CXXFLAGS env variables
+	set(C_BASE_FLAGS "-pipe")
+	set(CXX_BASE_FLAGS "-pipe")
+else()
+	# These are the default values
+	set(C_BASE_FLAGS "-march=native -pipe")
+	set(CXX_BASE_FLAGS "-march=native -pipe")
+endif()
 
 # For C and C++, the values can be overwritten independently
 if(DEFINED ENV{CXXFLAGS})

cmake/toolchain-gcc.cmake

@@ -11,9 +11,19 @@ option(GCC_ENABLE_SANITIZE_UNDEFINED "Enable -fsanitize=undefined" OFF)
 option(GCC_USE_GOLD "Use the gold linker instead of the standard linker" OFF)
 option(GCC_GENERATE_GDB_INDEX "Adds linker option to generate the gdb index for debug builds" OFF)
 
-# These are the default values
-set(C_BASE_FLAGS "-march=native -pipe")
-set(CXX_BASE_FLAGS "-march=native -pipe")
+# GCC does not support -march=native in RISC-V
+if(IS_RISCV)
+	# You do not need to pass a -march, passing nothing will make gcc to choose itself.
+	# If you want a specific set of instructions like vectors, set -march in CFLAGS and CXXFLAGS env variables
+	# Example for vectors: -march=rv64gcv
+    # https://gcc.gnu.org/onlinedocs/gcc/RISC-V-Options.html
+	set(C_BASE_FLAGS "-pipe")
+	set(CXX_BASE_FLAGS "-pipe")
+else()
+	# These are the default values
+	set(C_BASE_FLAGS "-march=native -pipe")
+	set(CXX_BASE_FLAGS "-march=native -pipe")
+endif()
 
 # For C and C++, the values can be overwritten independently
 if(DEFINED ENV{CFLAGS})

cmake/version.cmake

@@ -35,7 +35,13 @@ ELSE()
     SET(FSO_BINARY_SUFFIX "${FSO_VERSION_MAJOR}_${FSO_VERSION_MINOR}_${FSO_VERSION_BUILD}_${FSO_VERSION_REVISION_STR}")
 ENDIF()
 
-IF(IS_ARM64)
+IF(IS_RISCV)
+	IF(IS_64BIT)
+		SET(FSO_BINARY_SUFFIX "${FSO_BINARY_SUFFIX}_riscv64")
+	ELSE()
+		SET(FSO_BINARY_SUFFIX "${FSO_BINARY_SUFFIX}_riscv32")
+	ENDIF()
+ELSEIF(IS_ARM64)
     SET(FSO_BINARY_SUFFIX "${FSO_BINARY_SUFFIX}_arm64")
 ELSEIF(IS_64BIT)
 	# This is a 64-bit builds