Add riscv64-linux-android support

Add barebones riscv64-linux-android support.  This should be enough
to add riscv64-specific entries to Android.bp files, but can't
actually compile anything until there are riscv64 toolchains.

Test: arch_test.go
Change-Id: I0dcc7e797d9352dd38243be908a7f19004ff3db1
diff --git a/bp2build/cc_library_static_conversion_test.go b/bp2build/cc_library_static_conversion_test.go
index e3ea9a0..b47d1f1 100644
--- a/bp2build/cc_library_static_conversion_test.go
+++ b/bp2build/cc_library_static_conversion_test.go
@@ -836,6 +836,10 @@
             "not-for-lib32.c",
             "for-lib64.c",
         ],
+        "//build/bazel/platforms/arch:riscv64": [
+            "not-for-lib32.c",
+            "for-lib64.c",
+        ],
         "//build/bazel/platforms/arch:x86": [
             "not-for-lib64.c",
             "for-lib32.c",
@@ -867,6 +871,7 @@
 			"for-lib64.c":          "",
 			"not-for-arm.c":        "",
 			"not-for-arm64.c":      "",
+			"not-for-riscv64.c":    "",
 			"not-for-x86.c":        "",
 			"not-for-x86_64.c":     "",
 			"not-for-lib32.c":      "",
@@ -881,6 +886,7 @@
    arch: {
        arm: { srcs: ["for-arm.c"], exclude_srcs: ["not-for-arm.c"] },
        arm64: { srcs: ["for-arm64.c"], exclude_srcs: ["not-for-arm64.c"] },
+       riscv64: { srcs: ["for-riscv64.c"], exclude_srcs: ["not-for-riscv64.c"] },
        x86: { srcs: ["for-x86.c"], exclude_srcs: ["not-for-x86.c"] },
        x86_64: { srcs: ["for-x86_64.c"], exclude_srcs: ["not-for-x86_64.c"] },
    },
@@ -896,6 +902,7 @@
         "//build/bazel/platforms/arch:arm": [
             "not-for-arm64.c",
             "not-for-lib64.c",
+            "not-for-riscv64.c",
             "not-for-x86.c",
             "not-for-x86_64.c",
             "for-arm.c",
@@ -904,15 +911,26 @@
         "//build/bazel/platforms/arch:arm64": [
             "not-for-arm.c",
             "not-for-lib32.c",
+            "not-for-riscv64.c",
             "not-for-x86.c",
             "not-for-x86_64.c",
             "for-arm64.c",
             "for-lib64.c",
         ],
+        "//build/bazel/platforms/arch:riscv64": [
+            "not-for-arm.c",
+            "not-for-arm64.c",
+            "not-for-lib32.c",
+            "not-for-x86.c",
+            "not-for-x86_64.c",
+            "for-riscv64.c",
+            "for-lib64.c",
+        ],
         "//build/bazel/platforms/arch:x86": [
             "not-for-arm.c",
             "not-for-arm64.c",
             "not-for-lib64.c",
+            "not-for-riscv64.c",
             "not-for-x86_64.c",
             "for-x86.c",
             "for-lib32.c",
@@ -921,6 +939,7 @@
             "not-for-arm.c",
             "not-for-arm64.c",
             "not-for-lib32.c",
+            "not-for-riscv64.c",
             "not-for-x86.c",
             "for-x86_64.c",
             "for-lib64.c",
@@ -930,6 +949,7 @@
             "not-for-arm64.c",
             "not-for-lib32.c",
             "not-for-lib64.c",
+            "not-for-riscv64.c",
             "not-for-x86.c",
             "not-for-x86_64.c",
         ],