linux: Don’t make assumptions about the CPU revision

This code that works out the name of the CPU being built for is most
likely going to move out to be used more generally and for Android. It
should nail down the CPU name correctly when possible. Previously,
32-bit x86 always showed up as “i686” and 32-bit ARM always showed up as
“armv7l”.

Bug: crashpad:30
Change-Id: Ifd4b91f30062f5ef621a166f77a732dd8a88a58e
Reviewed-on: https://chromium-review.googlesource.com/458118
Reviewed-by: Robert Sesek <rsesek@chromium.org>

util/net/http_transport_libcurl.cc

@@ -48,28 +48,64 @@ std::string UserAgent() {
     // as the user process’ architecture. On Linux, these names are normally
     // defined in each architecture’s Makefile as UTS_MACHINE, but can be
     // overridden in architecture-specific configuration as COMPAT_UTS_MACHINE.
-    // See linux-4.4.52/arch/*/Makefile and
-    // linux-4.4.52/arch/*/include/asm/compat.h. In turn, on some systems, these
+    // See linux-4.9.17/arch/*/Makefile and
+    // linux-4.9.17/arch/*/include/asm/compat.h. In turn, on some systems, these
     // names are further overridden or refined in early kernel startup code by
-    // modifying the string returned by linux-4.4.52/include/linux/utsname.h
+    // modifying the string returned by linux-4.9.17/include/linux/utsname.h
     // init_utsname() as noted.
 #if defined(ARCH_CPU_X86)
-    // linux-4.4.52/arch/x86/kernel/cpu/bugs.c check_bugs() sets the first digit
-    // to 4, 5, or 6, but no higher. Assume 6.
+    // linux-4.9.17/arch/x86/kernel/cpu/bugs.c check_bugs() sets the first digit
+    // to 4, 5, or 6, but no higher.
+#if defined(__i686__)
     const char arch[] = "i686";
+#elif defined(__i586__)
+    const char arch[] = "i586";
+#elif defined(__i486__)
+    const char arch[] = "i486";
+#else
+    const char arch[] = "i386";
+#endif
 #elif defined(ARCH_CPU_X86_64)
     const char arch[] = "x86_64";
 #elif defined(ARCH_CPU_ARMEL)
-    // linux-4.4.52/arch/arm/kernel/setup.c setup_processor() bases the string
+    // linux-4.9.17/arch/arm/kernel/setup.c setup_processor() bases the string
     // on the ARM processor name and a character identifying little- or
     // big-endian. The processor name comes from a definition in
-    // arch/arm/mm/proc-*.S. Assume armv7, little-endian.
-    const char arch[] = "armv7l";
+    // arch/arm/mm/proc-*.S.
+#if defined(__ARM_ARCH_4T__)
+    const char arch[] = "armv4t"
+#elif defined(__ARM_ARCH_5TEJ__)
+    const char arch[] = "armv5tej"
+#elif defined(__ARM_ARCH_5TE__)
+    const char arch[] = "armv5te"
+#elif defined(__ARM_ARCH_5T__)
+    const char arch[] = "armv5t"
+#elif defined(__ARM_ARCH_7M__)
+    const char arch[] = "armv7m"
+#else
+    // Most ARM architectures fall into here, including all profile variants of
+    // armv6, armv7, armv8, with one exception, armv7m, handled above.
+    // xstr(__ARM_ARCH) will be the architecture revision number, such as 6, 7,
+    // or 8.
+#define xstr(s) str(s)
+#define str(s) #s
+    const char arch[] = "armv" xstr(__ARM_ARCH)
+#undef str
+#undef xstr
+#endif
+#if defined(ARCH_CPU_LITTLE_ENDIAN)
+        "l";
+#elif defined(ARCH_CPU_BIG_ENDIAN)
+        "b";
+#endif
 #elif defined(ARCH_CPU_ARM64)
     // ARM64 uses aarch64 or aarch64_be as directed by ELF_PLATFORM. See
-    // linux-4.4.52/arch/arm64/kernel/setup.c setup_arch(). Assume
-    // little-endian.
+    // linux-4.9.17/arch/arm64/kernel/setup.c setup_arch().
+#if defined(ARCH_CPU_LITTLE_ENDIAN)
     const char arch[] = "aarch64";
+#elif defined(ARCH_CPU_BIG_ENDIAN)
+    const char arch[] = "aarch64_be";
+#endif
 #elif defined(ARCH_CPU_MIPSEL)
     const char arch[] = "mips";
 #elif defined(ARCH_CPU_MIPS64EL)