Add RISC-V support

Upstream-Status: Submitted [https://bugzilla.mozilla.org/show_bug.cgi?id=1318905]

Signed-off-by: Ricardo Salveti <ricardo@foundries.io>

diff --git a/build/autoconf/config.guess b/build/autoconf/config.guess
index d5d667d..1277a86 100755
--- a/build/autoconf/config.guess
+++ b/build/autoconf/config.guess
@@ -1029,6 +1029,9 @@ EOF
     ppcle:Linux:*:*)
 	echo powerpcle-unknown-linux-${LIBC}
 	exit ;;
+    riscv32:Linux:*:* | riscv64:Linux:*:*)
+	echo ${UNAME_MACHINE}-unknown-linux-${LIBC}
+	exit ;;
     s390:Linux:*:* | s390x:Linux:*:*)
 	echo ${UNAME_MACHINE}-ibm-linux-${LIBC}
 	exit ;;
diff --git a/build/moz.configure/init.configure b/build/moz.configure/init.configure
index 6fe6591..56e6730 100644
--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -362,6 +362,9 @@ def split_triplet(triplet):
     elif cpu.startswith('aarch64'):
         canonical_cpu = 'aarch64'
         endianness = 'little'
+    elif cpu in ('riscv32', 'riscv64'):
+        canonical_cpu = cpu
+        endianness = 'little'
     else:
         die('Unknown CPU type: %s' % cpu)
 
diff --git a/mfbt/double-conversion/utils.h b/mfbt/double-conversion/utils.h
index 15dd4bf..4f37218 100644
--- a/mfbt/double-conversion/utils.h
+++ b/mfbt/double-conversion/utils.h
@@ -60,7 +60,8 @@
     defined(__sparc__) || defined(__sparc) || defined(__s390__) || \
     defined(__SH4__) || defined(__alpha__) || \
     defined(_MIPS_ARCH_MIPS32R2) || \
-    defined(__AARCH64EL__) || defined(__aarch64__)
+    defined(__AARCH64EL__) || defined(__aarch64__) || \
+    defined(__riscv)
 #define DOUBLE_CONVERSION_CORRECT_DOUBLE_OPERATIONS 1
 #elif defined(_M_IX86) || defined(__i386__) || defined(__i386)
 #if defined(_WIN32)
diff --git a/python/mozbuild/mozbuild/configure/constants.py b/python/mozbuild/mozbuild/configure/constants.py
index dfc7cf8..4f8d666 100644
--- a/python/mozbuild/mozbuild/configure/constants.py
+++ b/python/mozbuild/mozbuild/configure/constants.py
@@ -48,6 +48,8 @@ CPU_bitness = {
     'mips64': 64,
     'ppc': 32,
     'ppc64': 64,
+    'riscv32': 32,
+    'riscv64': 64,
     's390': 32,
     's390x': 64,
     'sparc': 32,
@@ -79,6 +81,8 @@ CPU_preprocessor_checks = OrderedDict((
     ('s390', '__s390__'),
     ('ppc64', '__powerpc64__'),
     ('ppc', '__powerpc__'),
+    ('riscv32', '__riscv && __SIZEOF_POINTER__ == 4'),
+    ('riscv64', '__riscv && __SIZEOF_POINTER__ == 8'),
     ('Alpha', '__alpha__'),
     ('hppa', '__hppa__'),
     ('sparc64', '__sparc__ && __arch64__'),